Hi Ralph and everyone else,
I've just released a modification to the RSS Feed plugin that adds Ecommerce tags to the output.
By default it generates the same output as the original plugin, you have to pass the "?ecommerce=1" parameter to get the new behaviour. I've also reworked (optimized) the SQL on the plugin, now there's only one query to get all the needed data (please test).
The plugin can be downloaded from the usual place.
More info on my site. Sample (live) feed here.
Regards,