ZBrushCentral

Round Edge problem

I made low poly bust in 3DSMax which I have already sculpted quite a lot in ZBrush. Now I have stumbled across a problem, I would like to make a hard edge, like a tight hat edge but with almost square angles.

My mesh topology is already set so if I use masking with inflate it gives me a jagged result.

I also tried Polypaint > Polygroups from Polypaint > and then Group Loops. This method makes nice round edges but it also require to delete all the lower subdivision levels which I want to retain as this is supposed to be a low poly model with normal maps and all that stuff.

Has anyone have any good ideas how can I go around this problem?