Your paragraph seems a tad confusing, MED is advertised to a neigbour, neigbuors have to explicitly configured to accept to send MED.
If iBGP derived route then the MED will take the value of the IGP, and advertise that out to iBGP peers. As for the next hop it HAS to be known via an IGP, the prefix's associated with that NEXT_HOP will or can have a MED, Weight etc value to determine the best path to use.
MED is a transitive atttribute and generally exchanged between AS's
May i ask what it is you are trying to achieve.. load balancing..???