I used to run a Branch of William Hill's before I came to Korea. Strange bets are always possible. It isnt the managers jurisdiction to refuse you a strange bet. They can always call their odds compiling's offices. If they refuse you outright then they are bullshitting you or else its a busy time of the day for them. They do work pretty hard (in large city centres anyways).

If they dont comply then threaten them with the customer service hotline. The manager of a branch of a bookies aint a fun job.

I ran away to Korea!