I'm not 100% familiar with the difference in e53 seat control modules...but is the seat control module designed the same in the comfort & sport seats? If yes, then remove the seat control module from your comfort seats and swap it with your new sport seats. Instead of pulling the whole seats in and out...just swap the driver's seat control module that's mounted in to the plastic seat cover (surround).
<b> EDIT:
</b> looking at the part database diagram & finding an image of the comfort seat control module...then at the driver's seat switch in my X5 which just has the regular seats with lumbar...looks like the e53's comfort seat switch is different than the switch for the seats that don't have the upper articulating back & electric head rests. There appears to be an extra little button built into the main seat control module that has 4 arrows on it (headrest up/down + articulating upper back section forward/backward). This is not how the e38/e39 driver's seat control module is designed...the upper articulating back on those models has a separate switch that controls that function. 
But I still wonder if you can use this switch anyway...if there's no wiring harness for the electric headrest & articulating upper back...that shouldn't stop the seat memory and the other seat movements from working. I'd still give it a try...and see if the module from your comfort seats will retain their memory when installed in the new sport seats. Its just that the headrest and upper back won't be electrically activated anymore.
The seat belt tensioners have an explosive charge that goes off in a crash that keeps the seat belt pulled tight to prevent the passenger from moving toward the dash. So if the seats came from a vehicle that was in a crash...as mentioned above...you may need to use your old tensioners as well as swapping over the seat control module. Find out if the SRS/MRS system was fully functional in the X5 that you got your seats from...and if no one was sitting in the front passenger seat...then that explosive shouldn't have gone off...and only the driver's side needs to be replaced. If the SRS light was on in the crashed X5...then the front passenger seat belt tensioner went off as well regardless if someone was sitting in the seat...so that one needs to be replaced as well.
item
#13 in the diagram below is the front seat tensioner...the explosive is built into this item...you can see the yellow explosive in the 2nd image below.
