Projects security for revenue projects

We are looking at implementing projects security for internal projects. What this means, keymembers who are assigned to internal projects [is a project type] will be able to see only internal project amounts. Having said this if a keymember is applied to other types of projects [i.e capital project], then they should be able to access those projects as well via PSI. 

I have looked at role based security but my view is that this functionality is not quite what we want. Appreciate if some one can suggest a standard functionality to manage this scenario,