I've never seen any kind of adapter. Most people have a spare GI rhino so maybe you've got one or know somebody that does.
If it were me I'd sell the G-11 and use a GI rhino while saving up for a proper G-24 (and I'm king of being thrifty).
The G-24 with wilcox dovetail is that much of an upgrade! Plus, if you ever upgrade to duals, you'll already be setup with a G-24