Hi Peter,
Yes, we know that plugin, and some features had been already integrated in terms of the search feature. Filtering by user meta is on the upcming features list, it is not yet finished. Unfortunately it is not possible to simply integrate it via a few lines of code, both the back-end, the search, the query and the post process classes need to be re-worked in order to execute it correctly.
I will move up this request to a top priority, so we will try to finish it quicker and include it in the upcoming minor release. We have a release scheduled by the end of the next week, maybe a bit sooner.
There is a public upcoming feature tracker, if you want to see what we have planned: https://trello.com/b/BUNOEob3/asp