Just throw your old GPS away and buy the “New and Improved” version. It is the American way.
One of the problems is that there may be no effective way to come up with the "New and Improved" version without major changes. Those people who understand the design constraints of RF filters know that it's technically possible to have rejection capabilities of the scope needed to keep LightSquared ground-base transmitters from causing problems...but it may not be economically feasible, or impossible to implement the filters so GPS units will fit in your pocket. There is also the question about shielding the RF portion of the unit, and preventing RF leakage through the power connector or accessories connector.
In short, this is not a problem that can be fixed by GPS vendors just slapping a Band-Aide on their existing designs.
The obvious solution is for LightSqared to swap spectrum space with someone, instead of asking for a waiver of the rules that will impact the GPS industry. (Or, they could put up more satellites.)
It's the job of the person with the transmitter to mitigate inference problems with other licensed users, and GPS is indeed implemented by a licensed user. LS has to be the one to deal with it, or stop operation of ground-based transmitters. Period.
The real issue is well stated in your post. See my post at 26.