For some odd reason I was simply -unable- to get select() to work properly on filehandles that encapsulated a process. select() was actually my first port of call, and after spending several hours without luck, I switched to the method outlined above.
Unfortunately it's been a few weeks since I tried the select() method, so I do not recall the specifics - I've used it a thousand times with TCP sockets, so it's not like I've never used it before... I'm sorry, I just can't remember why it didn't work properly. I'll see if I can dig up the source code to remind myself!

Thank you, however.