When storing a message, the entire contents (including any attachments) are stored, and it's not possible to store the message without its attachments.
Another option would be to link to the original message rather than storing in UR. The message content will still be searchable and displayed in UR.
http://www.kinook.com/UltraRecall/Ma...ronization.htm
http://www.kinook.com/UltraRecall/Ma...recontents.htm