Sorry for the delay, but yes I think the solution here is what you're getting at. I used the XOG files attached in the post linked to up above. From what I recall (it's been awhile!) that XOG created a portlet, a page containing that portlet, and a new link type. I took the Document virtual attribute on the project page (believe its OOTB, might be an addin) and changed it to link to the new "URL REdirection" link action, which gives you one parameter option, which I set to our sharepoint URL. The portlet contains a bunch of javascript, I had to tailor this to go to the SP site (the attribute is relative like "/ClarityProjects/PR######" so I have the JS add the full SP domain in front of it). It does show clarity briefly before it redirects, but we found that acceptable, and noone has ever complained about it thus far.
if (go2url.indexOf("/ClarityProjects") > -1) {
go2url = "http://fulldomain"+go2url;
}
window.location = go2url;