I was really hoping that this would work
The stale shares you're referring to are because of the aforementioned long-polling issues. Nobody is sure what makes it work, or not work, through the current codebase. The best suggestion I can give you is to run something like PHProxy at http://url.of.your.minining.proxy/phproxy/ and edit the code to send out this URL to your miners, rather than trying to use the in-built broken proxying code. At least I think that'll work, from what I recall of the code and the way that LP works. If you go this route, report back and let us know how it works out.