I have gone over every meeting of Rand's with Fel in order to try and determine who could have known about their dicussions concerning the DO's prison. There were only two people that I found that could have possibly known. Jalani and Dedric were guarding Rand the day that he came to have his first meeting with Fel in LoC. One of them might have overheard what they were discussing. I think that the prime candidate is Jalani. Dedric could be, but he is too minor of a character (in my opinion) to be suddenly brought into the story now. I believe that Jalani is a darkfriend, and passed the information on, until it reached someone (probably Shaidar Haran) who sent the gholam. It could have been Sammael, but I believe that it is highly unlikely that the forsaken know the nature of the seal and the patch.