Here's my crazy proposal:
1) Keep only the 1000 BTC we've already moved into offline wallets
2) Use the remainder of our BTC to purchase MSC over the next few months on the distributed exchange
3) Pay all future bounties exclusively in MSC
4) Keep half of our MSC money for a rainy day and/or future distributed bounty system
5) If our rainy day fund becomes excessive, we can always vote to lower the ratio later
I realize that this would potentially make all of our existing investors absurdly wealthy, but, well, the stated purpose of the Mastercoin Foundation is to serve the holders of Mastercoins, and I'm having a hard time seeing this course of action as anything but a huge positive for them, as long as we do it transparently and over a long enough period of time that nobody who wants to sell to us is left out.
Also, MSC prices would probably go up to the point where I'd sell 1% and quit my job to work on MSC, which I hope would also be in the best interests of our investors.
No promises