If you want the same register as a baritone then you have two practical problems and one from the law of physics.
1. An unwound G would be too thick to sound or intonate properly. You might find a wound string which was usable. Low D will be too thick to work, even wound. The E already exists in the soprano set, and for both the D (re-entrant) and B you could use a C string, tuned appropriately. Or an E tuned down for the D.
2. Your nut slots will all need reworking to fit.
3. The physics problem is that C is close to the lowest note which will sing out on a soprano body. So your G will be weak. OTOH, a wound string often rings louder than an unwound, so it might not be too bad.
For the wound G, try a classical guitar A or possibly D.
Good luck if you try it, and let us know.