Hi vallesm77,
Check this related thread for some options to parse the virtual name from the path:
http://devcentral.f5.com/Community/GroupDetails/tabid/1082223/asg/50/aft/2158968/showtab/groupforums/Default.aspx2234683
You might also consider updating your iRule to use the full virtual name as the data group should have a folder as well.
Also, if you're running on a CMP capable platform you should try to avoid using global variables like "$::defaultValue". You can set $static::defaultValue in RULE_INIT instead:
http://devcentral.f5.com/wiki/iRules.static.ashx
Aaron