Ewfflyer

As a CFI, I'd say you're putting a lot of trust into someone else that's not rated. If this student needs practice, they should do it solo, or from the right seat. You are not even a commercial pilot, let alone a CFI, so honestly you have no business in the right seat. Just my opinion, take it as is

pilotinsky

Start you instrument or commercial training w/CFI, and ask your friend sit in the back seat.

Never trust student pilot on control; from experience as CFI.

WEACLRS

I'm also a Flight Instructor and a FAA Safety Team Representative. DO NOT DO THIS! This type of activity has been proven to be dangerous. While there may not be a regulation specifically prohibiting it, the FAA will consider you the PIC due to your more advanced certificate and will find you in violation of 14 CFR 91.13 should there be an incident or accident and they become involved. If you do a search of the NTSB accident data base you will find accidents involving this type of scenario, both in the GA world and unfortunately in the 121 world (think Pinnacle).

I think if you were to look closely at your rental agreement you'll find your FBO/insurance company will require you to be in the left seat. Check with your FBO.

Many airlines require their dual-seat qualified pilots to either fly from both seats annually in the simulator to remain qualified, or to be a qualified check airman. They don't do this "just because", trust me.