I hate to be contrary, but if you solder the sight, once it's there, it's there. If it's a non-adjustable sight, there's no way to drift for windage. It could take many resolder operations and subsequent range trips to get it right.
I see nothing wrong with cutting a shallow dovetail in the round portion of the barrel for the sight, assuming it's a dovetailed sight to begin with. The dovetail doesn't need to be as wide as the base of the sight, just enough to anchor it in place. I've cut them in round barrels for old .22s and it's no problem.
Another thing to think about is that your sight may sit lower on the round portion and you may need to file off a little from your front sight to get the correct elevation.