i have a singlespeed 29er that i run fixed with a tomicog pretty often. the ss side of my rear hub is a splined cog & spacers on a freehub & i have a ss crankset with the ring on the inside.

unfortunately, i lent that bike to my kid & have not been able to get him to return it so i can't measure but if i remember correctly, i think it is a 50mm chainline when it is set-up ss. when i am in the mood to go fg mtbing i just put the tomicog on, flip the wheel, & hit the trails. it is not a perfect chainline but it has never been a problem.

op...as long as you have the chain & derailler thing figured out, there's no reason your plan should not work out easily.

M_S is right, go ask about this over in the ss forum on mtbr where you will likely get better info than suggestions to buy a 2nd wheel or a vertical stand & another bike

have fun & good luck...