Is this even posible?
What gauge would I need?
"I wanted water but I'll walk through the fire"
On a steel string guitar? Should be possible without hurting the guitar, but I'm not sure the strings will fit well in the nut (+saddles). Why would you do this?
You can buy ball-end nylon strings... However, nylon has about half the tension of steel, so the guitar would sound muted at best.
The nut slots for the treble strings would be too small as well.
Finally, due to the low tension, you'd likely get a lot of fret buzz.

Not a good idea.....