My first assumption would be that it
could work if...you got the PM-SM (power module-seat module) w/memory for the right side (just as you supposed)...but you'd also need to change the door switchblock module, too.
I don't
think the data being sent/received over which ever communication bus it would travel...would get confused...because there's multiple data already being sent all over the vehicle...so each module probably has some type of indentification marker.
The seat memory is controlled thru the driver's door switchblock module, so you'd probably need to order the correct RHD (driver's) door module for the seat memory to function.
This diagram's illustration is more for the e38/e39...but the e53 is set-up similarly:
