@hyena: well, i'd stick to the truer form of bubu myself. i feel like condemning abuse of bubu-ing (especially) and other uncalled-for variations. however, i have to admit in every language there must be at least one word of way of saying that is so bubu-compelling, and with such an hilarious result, that exceptions might be made.
as for the plural, i'd suggest to avoid using it altogether. 'bubu' is a substitute for two syllables, regardless of the word's ending, be it plural, feminine or whatever your language of choice feels like ending a word with.
rahvin. (for the bu, for the bu, for the bubu)