Still around Naroghin?
In case you are, the only other leads I know of besides getting the module system as Lup offered is:
1) To use the 'Cheats' menu to 'Downgrade' (It's an actual option if I remember correctly) the Economy and Military levels of Custow so that they are both at zero. Wickedshot included cheats that allowed us to pretty much visit any settlement we like and change (upgrade/downgrade) their economy and military levels if we want to.
Then, to follow along your idea of making a 'Custow' like settlement someplace else, head towards a settlement you want acting as Custow did and upgrade the Economy and Military levels to the maximum possible -- that'll give it the same parameters/settings as Custow had to become a big city/town settlement.
Unfortunately, the new settlement you pick to replace Custow's effect on the early game will have it's own different hero parties attached to it. Wirt of Gonace for example is always patrolling and returning to Custow, and the new settlement you choose to act as Custow will have different heroes patrolling around and dropping off prisoners, etc. Thus, you'll most likely have different chances of certain factions starting up at your new 'Custow-replacement-settlement' than at the original Custow.
2) I'm not fully sure on this one, Lup_Alb or someone who knows the module stuff might need to clarify if I'm wrong or right, but I remember there was a program/method to moving around settlements on the map in a very simple point'n'click manner without needing to do any hex-editing of numbers in the python files/module for the game. Lots of different mods change the location of stuff on the world map all the time, after all, so I vaguely remember doing a bit of research and finding out there's some kind of simple world map editing program they all tend to use to do that kind of work. That's the best information I got on that matter, hope someone else can shed some more light for you here if your interested.