I'm pretty lazy with that and tend to assume an extract potential of 77% for all malts ( don't know if this is equal to 36 pppg, but it will be close). This is not necessarily correct but gets me close enough.
Most of the time I don't even use efficienctly directly but simply use the grist weight that I used on a past beer which had the same or a similar OG. For example I know that I need to use a grist weight of about 4.2 kg if I want to make a 12 Plato beer with my system. I then know what malts I want to use at which percentages which gives me the individual weights for the malts.