There is no such plugin or ability yet (or any expression of need for such an ability).
If you know how to code in PHP you might look at the experimental tag filter I made inside of the Hidden-Forums plugin to see how such a query would be done. You could then use the query to create a custom view for the topic results.
Ok, I’ll take a look at that. I’m actually planning on converting my phpBB2 forum over instead of moving to phpBB3. I have made mods for phpBB2 and would like to make the same plugins for bbPress, but not if they already exist.
I just realized I should also point out that my Related Topics plugin will also give the greatest weight to other topics with the most tags to the one you are on. It essentially does a multi-tag search internally.
I don’t know what would be a good user interface to pick multiple tags but the query and resulting view are fairly straightforward to code.
