I think the current Pay N Spray branches (being all across the city) works quite well already.
And for the same reasons that I wasn't too keen on this idea when you told me in-game I still don't think we'll need such a feature - mostly as they are already covered within other businesses.
Car bombs for example are only exclusive to Phill's Place, and it gives that business an upper hand and would probably be not too happy with competition.
And I think it could be more "illegal" - it doesn't seem too bad to me, if you see what I mean.
Perhaps it could be a little like an off market car garage, but I am not sure how well it would be put to use.