You could always get a punch. I don't know where you would find larger guillotine cutters. I've never had a problem since I try to take off as little of the cap as will allow me a good draw. I hate when cigars unravel on me.
You could use a 9mm, 40, or 45 cal brass for a punch. Use a chamfer tool on the case to create a sharper edge. Just clean it good, gunpowder residue doesn't go well with a good stogie.
There are some larger puches on the market. I have a xikar and a vector. Both have done well for up to 54 ring cigars.
I just use the Swiss Army Knife on my key chain to carefully cut a circle out of the cap. Works great, I've probably cut a couple hundred cigars that way, and have maybe damaged 2 a little. Works better than my Xikar except on torpedoes.