Dr_A: I'm not quite sure what you mean here, or why the need! Being RS232 units, with resulting multiple hi/lo 10101010 etc data streams, I guess an extended 11111111 could be sent. Surely however an attached PICAXE can just suitably decode the serial generated by a locally switched high, & then make an output high at the far end?
I've written an intro. article for the July(?) Silicon Chip on these units, which IMHO ultimately show great potential for "2nd generation UHF telemetry", especially since the quality SMA antenna socket supports higher gain antenna. Even a "cotanga" Yagi of course gives ~6dB gain ( enough for range doubling), so 1 at each end will give x4 the omni-directional range for a point to point link-good for maybe a few km LOS.
Aust/NZ distributors may well emerge, especially if they retail at ~Aust$10 each, & since each HM-TR is both a tx & rx ,they're ~½ the price of 1st generation Jaycar etc offerings. HopeRF have been most responsive to ideas & distribution, so hands up any Ozzies who'd go for a couple at say Aust$20 a pair? Stan.