I don't know the code that is producing the error and I have not tried this so this is just a guess...

The problem is presumably that the promotion code needs to follow the chain of dependencies to make sure they all get promoted. How about making as many as possible of them explicit dependencies of your main package? If you are lucky, that will mean it doesn't have to go very deep in its search.

So, for example, assume cups depends on pkg-a which depends on pkg-b which depends on pkg-c which depends on pkg-d which depends on pkg-e. Try listing all of pkg-e pkg-d pkg-c pkg-b and pkg-a as explicit dependencies of cups. And make sure the lower level dependencies are listed earliest in the list so that they do not trigger deep searches themselves.

I have no idea whether it would work (it depends if the dependency search optimises not bothering to look at packages it has already seen) but it might be worth a try.

The real fix, by the way, is to log a bug report on the promotion code (and once you have done that you could contact Niels by email to see if he can help with it at all).