It may be that people who initially consider donating in bitcoins will change their minds and donate dollars instead.
The presence of this consideration in your list suggests that perhaps you or some of your readers do not realize that at present, there are web sites similar to foreign-exchange windows where SIAI can probably easily convert bitcoins into dollars.
Now you can donate to Singularity Institute using Bitcoin.
Currently Bitcoin mining appears to be profitable as only bubble economics can be. Already some Less Wrong users have purchased GPUs and started mining Bitcoin. Please consider sending some Bitcoins to SI at address 1HUrNJfVFwQkbuMXwiPxSQcpyr3ktn1wc9
2014 Edit: Please donate Bitcoin by using the Bitpay link on MIRI's donate page. Thanks!