Arpita
Say a very straight NO but in a very polite manner.
If this employee is using computers you can easily say this, It's the System admin seating arrangement and it has been done in a very calculative way hence it not possible to gave a change in place. Today if you say yes then, its for vastu today, tomorrow he may come for numerology, later for good time and so on and so-forth. This will encourage other employees also to ask the company to favor them on their superstitions.
Make a clear statement on NO and make sure you don't tend to say anything on his religious/ belief/ faith front. So clearly phrase your words and give it straight and don't try any negotiation even if the employee tends to do.
Handel this with care.