This would be great.
Until it is created there is a work-a-round. You create a custom trade search as you would now. Add in whatever European countries you want to include in your search. For reference the biggest countries from the user survey viewpoint are:
UK, Spain, Germany, Netherlands, Belgium, Sweden, Finland, Greece, Poland, Italy, Portugal, Denmark, France, Hungary. This isn't a full list, for example UK users could also be in as England, Scotland or Wales.
Here is an example (I think this is generic, not specific to my user ID):http://www.boardgamegeek.com/trade/custom?action=customsearc...
Then you save the resulting page as an entry in your Quickbar. You can then click on that link at any time for an instant check on items for trade in those countries matching an item on your 'for trade' list.