I recruit specifically for each of those 4 positions you mention. Then i have my practice plans set to account for both types of RB for example. Currently, it is the only way to do it.
The good thing, i say very sarcastically, is that we know putting more than 8-10 minutes into a formation practice is a waste of time. So, unless you practice every offensive and defensive formation, you have plenty of time for individual practice categories.