I did exactly the same thing -- finding an appropriate temp to fill in for me during maternity leave.  Because my boss was a VP, this had to be a top-notch person.



The process was to bring in a temp for training (getting to know you, etc.) for 5 days, then she/he would be on call for when they needed to come back.  



As I remember it, 4 temps came and I discounted them on day 1.  Then the 5th temp was awesome.  She came in on a Thursday, was there on Friday, and ds was born on Sunday!  I think he was waiting to make sure the sit at work would be ok - ya think?



Good luck!