I've always assumed that the pmists use of 'bosh' comes from that bit in The Timelords' Doctorin' The Tardis where the dalek-voice goes 'bosh bosh bosh!' -- ie that it's quite specific to this group of people. But "bosh bosh bosh bosh" is also quite common onomatopoeia for four-to-the-floor bangin' techno.

'bish bash bosh' is quite a common cockney phrase, it sort of indicates that something will be fairly swift to knock together? And then of course to Edward Lear or someone 'bosh' meant 'nonsense'.