I encourage you to rethink the wallpaper analogy. Bookers and restauranteurs will sniff that 'tude a mile away and won't touch it with a 10 foot poostick...unless of course, they want wallpaper.

Playing music is a fine art. Crafting a compelling musical performance that
fits the needs of different venues is part of that art, as is the business
smarts and savvy it takes to figure out how to get paid while doing it.

Remember "PLAY THE ROOM"

Describing your act to potential employers as "bland aural wallpaper" probably won't help. Why would someone want to hire you when they could just pop some musak on their house iPod?

I might also scout out places that aren't doing music but seem like they might be a good place for what you to do. Particularly if you have your own small P.A. you can bring in (or if you don't need one), you might be able to sell them on the idea of having music in the venue. Might not be lucrative at first (good chance you might need to do it just for tips). But even if it's just a glorified night of rehearsal, it might still be a worthwhile opportunity to gain a reference, and polish your act.

If your thing is good and it starts being a draw for the venue, well, then you might be able to negotiate some guaranteed compensation. Or maybe you find that even though the gig itself doesn't pay, people who see you there want to hire you for their weddings and parties. So this restaurant gig becomes a loss leader for that. Or it helps you get other better paying gigs.

One final thought. I can't remember who said this, but I think it's true: You can often learn more from 15 minutes of performance than you do from 90 minutes of practicing. That doesn't mean practice isn't important. Without it, nobody ever gets to a point where they are worthy of other people's attention. But at a certain point, the only thing that makes performances better is the act of performing, even if the pay isn't great.

I don't know to be honest with you. I'd just look and see what restaurants are doing live background music and go in and ask them how they book their artists. Beyond that I'd say all the other first contact rules apply.

Good Luck.