Richard Hensman has just donated a custom button for RssFwd to plug into Google Toolbar. Unfortunately, the Firefox version of the toolbar doesn't support adding a custom button yet - which explains my delay in publishing this. Finally gotten to try it out today and it works pretty sweet :-) Thanks Richard!
If you have Google Toolbar installed, click on the icon below and give RssFwd a spin!
Note: it works exactly like the existing bookmarket,
Update: URL to toolbar button in google