Attach uploaded thumbnails to posts with csv?

I’m using CSV Importer to populate a catalog site. It works really well except it doesn’t have the facility to include an thumbnail url per post.

I’ve read a load of posts on this subject but none with an answer. The plug-in developer has it on his “to do” list …. but understandably, we all have todo lists…!!…. Unfortunately this is currently at the top of mine!!

Can anyone tell me how I can include the image urls in the csv file and then attach them to each respective post as the Featured Image? (preferably without resorting to custom fields as I want my client to use the Featured Image facility for single post updates the future…

Many thanks!