Attractiveness factor in Path Distance Allocation

I'm trying to find a way to do a path distance allocation while giving the input features (health centers) a kind of attractiveness factor.
I did some tests with the MarketAnalysisToolbox (update01262010) but I'm not yet convinced if this is the right tool. It was the only tool I found in this context though...

In the end I would like to have something like a probability surface showing for each point in the raster the probability to visit which health center. Do you know what I mean?

Has any one suggestions how I could reach this? When I take the probability surfaces the marketAnalysisToolbox is generating for each health center, how could I combine them in a way that it would make sense?

Thanks for your advice!
Nicole

PS: I don't have access to the Business Analyst but an advanced student licence for ArcGIS 10.1 Desktop