I didn't find it to hard to get DD to sleep for her appointment, I think I was lucky though.

I had my DD's tests at the royal cildrens hospital and they leave you in a dark quiet room to allow you time to get your baby to sleep, I turned up 10 minutes early and they showed me straight to the room (I am not sure if this is the same everywhere, but if they expect you to get your baby to sleep I expect they would).

I held her feed until we got there and fed her there and then rocked her in her pram, they were able to test her while she was sleeping in the pram. She did open her eyes a couple of times but they said as long as she stayed still it was ok, she drifted back to sleep though.

Best of luck with your test, it is nice to hear you were able to get an earlier appointment .