I've been looking into this (thanks abctc for the heads up, and of course to scor2k for the cool work) and it looks as clear and straightforward as it gets. I'm sure we can add a "Tip" button to the members information in posts.
Linking the "Nxt Account ID" profile field to a button that produces the right URL to receive a tip should be easy. Then we let scor2k's code do the magic and write a simple forum guide for anyone who wants to use a NxtTips account.