Well in Neverwinter Nights 1 the D20 based class and feat system can be very easily modified into Archetypes and Power Sets/pools. And the 6 player character races could be changed into six generic bodytypes instead. What I'm thinking would be these six. Athletic, Huge, Athletic-Tall, Huge-Tall, Athletic-Short, Huge-Short. With there being 2 Phenotypes for each body(race) the normal Phenotype could be made like when all body size sliders (excluding hieght and leg length) in CoX caharacter creater are at the center, and the large Phenotype could be made like when all the size sliders are all the way to the right (again excluding hieght and leg length). The 2 tall bodies could be about 8 feet tall, the 2 average bodies could be about 6 feet tall and the 2 short bodies could be about 4 feet tall. It wouldn't be as diverse as what the CoX character creater could do but it would provide a reasonable range and allow for huge female bodies too.
Neverwinter Nights 2 does have a better character creation process then NWN1 that includes size and girth sliders and it is possible to convert models from NWN1 (such as buildings from the modern city tileset) to be usable by NWN2
Here's a demonstration of some of the spell effects from NWN1 that could be reworked for use in power sets. Casting times, casting animations, area of effect, taget/s and many things about what these spells can do can all be altered.
http://www.youtube.com/watch?v=W4N7Ii1SSv0