I don't think it can be done, that is pass a law forcing disclosure of foreign company operations. The IRS can request a foreign company to provide information but they cannot force it.
They have to go by what Mr. Soros claims as income in his 1040 unless they can investigate other sources of income hs has not reported. And any such investigation requires cooperation with foreign governments. But privacy in banking is a gold standard for many international banks.
Speaking of privacy, I am for abolishing the IRS as it presently supports the personal income tax. I would like to see privacy for all Americans by abolishing the personal income tax and replacing it with the NRST. I'm not sure I will see such in my lifetime but I do like to read about it.
When Soros donated funds to the organizations such as MoveOn and others, he had to claim it was from personal funds. If those funds exceeded his income then he must claim the funds came from savings or investments. If from investments, he must claim the income from those investments.
I believe Soros is one of many greedy international market interlopers who never donates anything for free. I believe his 'donations' arise from revenue streams of his associates that are not reported to the IRS or any other government tax office.