Here's what I came up with a long time ago:
run mailto:your@email.com?SUBJECT=somesubject $+ $chr(160) $+ From: $+ $me $+ $chr(160) $+ Server: $+ $server $+ $chr(160) $+ Chan: $+ $active
Which produces a subject like this:
somesubject From:R1pl3y Server:washington.dc.us.undernet.org Chan:#channel $chr(32) wouldnt work so I used $chr(160) and it worx fine.
I hope this helps you in some way.