Can I run a dual crankset with a chain guide tensioner? We recently got a new mountain bike for my son via craigslist, it is a couple year old Transition Bottle Rocket and came with a E-Thirteen SS+ chain guide/tensioner.

He would like a lower gear for when we go up the hill to get to the good downhill trails.

Can we add a front derailleur and shifter to allow two front chain rings allowing a lower gearing for going up and one for when he goes down the trail.

He has a nice large 32 tooth on the rear cassette but still would like something a bit easier to spin up the hill
This is a common setup for many freeride bikes, as it allows uphill pedaling and a bash guard.  However only certain models of chain guide support this, and the one your son has doesn't officially (though it wouldn't hurt to try if you have a crankset to test; it might affect the derailleur ...).  The DRS is eThirteen's 'official' dual chain guide.