Interesting idea, but I'm not really convinced that a MAS would be very helpful in this case.

The idea of an insurance or MAS is to insure against devastating, low probability events that happen to people largely statistically independent. In this case the danger of margin calls moves identically for all MAS members. Meaning most of the time you will be paying a worthless service and once BTS price drastically drops the funds will be used up very quickly.

There is simply no way around the risk associated with taking a short USD (or whatever) position.