Clingfilm over the top of the wineglass - works in the ladies loo as well......
You used to be able to get hold of the 2 sachet refills for foam extinguishers. Partially inflated balloon around bend in loo to stop it flushing, one sachet in bowl, second sachet in cistern. Stanf back and wait for xx cubic metres of expanding foam....
All a bit messy though.