I think the answer depends on how, mathematically, you want to model dose-dependent absorption. You can easily create various PK models in SimBiology, as described here. One of the options for this is to model elimination with Michaelis-Menten kinetics. This would create dose-dependent elimination.
If that doesn't meet you needs, please share more details about how (mathetmatically) you want to model dose-dependent absorption.
I hope that helps.
-Arthur
