relative URL's in URL fields (e.g.homepage)

It looks to me like homepage, and other URL fields in the project description are forced to be full URL's (http://...). I'd like to encourage my users to put project pages (homepage etc) on the same server as the web site... which they could do, by filling in http://web.site.name/TheirProject - or whatever. But
a) I haven't fixed my web site name yet (!)
b) I'd just simply prefer relative links.
So, I guess you could use a more sophisticated reg-exp - but the names of user defined pages are pretty free, so the only reliable solution I can think of is to attempt to fetch the URL given?

For now, I've simply commented out the checks in project.inc (lines 235-239) but this is an unsatisfactory hack...

Am I missing something, is there a better way of achieving the same thing?
Will relative links break something else?

Cheers

Mark.