On a slightly sneakier front I have found something like this works quite well when you have to deal with Not Invented Here syndrome:
"I agree completely. You're correct and we need to write the modules ourselves. However, in the interest of producing a prototype quickly why don't we use these modules for the moment. They have a nice API which we can keep, and we can rewrite the internals later once we have things up and running."
"Later" never arrives. Especially when the expense of rewriting something that works becomes obvious.