Reg the advantage of betting against ourself for achieving a goal, check out sticKK - https://www.stickk.com/ and the psychological reasoning behind why it works is discussed here. - https://hbswk.hbs.edu/item/the-key-to-keeping-resolutions-betting-against-yourself.
Although coinciding, the basic premise of the problems stated by you and one being addressed by sticKK is different. You want to bring transactional commitment to casual bets and SticKK wants help fulfil personal commitments.
If a country's law allows such gambling, I think solving this problem might really be useful for those who are indulged in such casual bets. I wonder whether even sticKK would be allowed in countries where gambling is banned, even if its against ourself and the money goes to charity.