There is a Toolbox available on the matlab exchange server, which
includes models for DAC capacitor mismatch etc.:

http://www.mathworks.com/matlabcentral/fileexchange/loadFile.do?objectId=7589&ob...

Studying those models should help you to understand how capacitor mismatch
can be modeled.

Vector-based DEM like CLA, ILA, DWA etc. are easy to model.
You basically just need a vector where you store the indices of
the unit capacitors and rotate the position of the unit capacitors
according to the algorithm.

The book from Steyaert gives an overview over the most common DEM and explains how they work.
Yves Geerts Michiel Steyaert and Willy Sansen , Design of Multi-Bit Delta-Sigma A/D Converters, Kluwer Academics, 2002 .