Post Tags for Imported RSS Feeds

I use Yahoo pipes to aggregate multiple RSS feeds into one single feed and then import that into WordPress using Feedwordpress. I know that with Feedwordpress we can assign tags to all the posts syndicated by a single feed but I’d like to do something a little different.

Is there a way to structure an RSS feed so when it’s imported into WordPress, it will read the tags I’ve programatically assigned to the post.

For example, in a single RSS feed I’d import, I’d have Post 1 with the tag “Twitter” and in Post 2 I’d like it to be tagged “Facebook”. I’d use Yahoo pipes to work how which posts get what tag. I’d just need to know:
1. Can code be placed in an RSS feed that WordPress will interpret as a “tag”

2. If so what’s the syntax.