Yeah, it was very funny, as I was slipping her one she was moaning and whimpering and telling me to be quiet. I was actually silent, she was the one making all the noise

Only problem is, you couldn't ask for a 'double' booking because I think Dave must do all the texting, she speaks (and presumably writes) virtually no English.
I guess if anyone wanted to do it, the best way would be for one guy to make the booking, arrange to meet up with the other guy outside the main entrance, and then both present themselves at her door together. So long as it was two regulars, you'd just smile and wink sweetly, both offer up your £50s (£100 total) and see whether she took the bait.
I wouldn't mind betting it would work, and Dave'd be none the wiser!