I don't think you can. You might be able to convert the FLV to a SWF and
insert that instead.
Or maybe run the FLV from an HTML page and use something like LiveWeb to get
that live page into PPT. http://skp.mvps.org/liveweb.htm (Can't remember if
that would work from your harddrive or not, tho --you might need a streaming
server for the FLV to work from within HTML.)