Forgive me for disecting things, but perhaps you can tweak them to make something more singable.
I am the very model of a presidential candidate, From character to senator I know what to assassinate I lobby for the victims of injustice and adversities And care for those disabled when compared to my abilities.Up to this point, scansion is perfect. "Abilities" isn't a good rhyme for "adversities", however; for two words or phrases to rhyme well, the last difference between them should be the first consonant of a STRESSED syllable or the last consonant immediately preceding. In a solidly iamblic form such as "I am the very model of a modern major general", therefore, rhyming words should end with one or three rhyming syllables (note that every single rhyme in IATVMOAMMG is a triple-rhyme).
I've slept with movie stars and yachted with the Kennedys, I've copied their initials and shared in their amenities; And in the field of foreign wars my service is distinguished As soon as all the ugly rumors are extinguished.Scansion on these lines doesn't work. The first line is short by a pair of syllables. The second needs a syllable added somewhere between "initials" and "shared". The third could work if you threw a grave over the "e" in distinguished [to make it four syllables]. The fourth falls a pair of syllables short and also needs a grave to make "extinguished" four syllables.
I'm boarded prepped and schooled in snowy Switzerland, My haircuts and my facials put me out at least a grand My visage in the mirror never ceases to me fascinate I am the very model of a presidential candidate.First line is two pairs of syllables short; second is one pair short. I like the last two lines, though.
In short his visage never ceases to him fascinate He is the very model of a presidential candidate.First line is a syllable pair short. G&S style would be to repeat the previous couplet exactly.
I married very well, I did, and married nearly twice, The first was just for practice though the kids they say are nice. My first wife though depressive and annulled is still a friend, My second wife is richer still and is a major brand.All four lines scan well except that they come a pair of syllables short.
Opinions, like my marriages, I always form in pairs, I'm married to ideas when they belong to millionaires; So right and wrong are nuanced and I have my haws and hems, I'll never rush to judgment like Lord Hamlet on the Thames.Again, scansion is clean except for line length (one pair short each).
I am the very model of a presidential candidate In matters war and peaceful I can spin and vacillate When I am president at last, we will surely will have peace Unless the right wing leader of some Haiti or some GreeceLines 2-4 scan well but come out a syllable-pair short.
Stirs up an insurrection that requires my attention Or extra votes are needed just before the next election. In which case I will castigate severely the aggressor. Or maybe delegate the task to the U.N. or my successor.The first two lines will scan properly if "attention" and "election" are read as four syllables each: "att-en-ti-on". The third and fourth lines fall a syllable short right at the end.
Because most of the scansion is pretty good, it shouldn't be too hard to tweak things so as to fully fit the double-octameter pattern of G&S. Although IATVMOAMMG is perhaps the most parodied of the G&S songs, it is also one of the most rigid in form even though very few parodies properly handle the triple-rhymes. Something like "When you're lying awake with a dismal headache" isn't quite rigid in form, since while most lines have 22 syllables, some have 23 and some have 21. By contrast, every line on IATVMOAMMG has exactly sixteen syllables except for the lines in which a pair of syllables is repeated (which thus have 18).
One thing for which I will give you credit is that, while many of the lines fall a syllable-pair short, the word stresses for the most part work. This is much better than some attempts I've seen where the word stresses come across as basically random.