I can kinda see what you mean but for an adapter to only be able to have 3 bolts is outrageous!
I'd definitely not recommend but I'd definitely do it 10 mins to a garage as Tweed says.
Let's not get into 2 bolts on 4x100

Also done 4 on each wheel when picking up a car who's wheel had fallen off due to a tyre place not tightening lugs. Took one out of each other wheel. 3 on one wheel and 4 on the other 3.
Not an issue. But as said there is a reason for having 5 and the bolt heads and the wheel where the bolt heads meet get extra wear and oval when say 2 or 3 are fitted.