This results in:
Players 1st Half 2nd Half Total
aa 10 30 40
bb 20 20 40
cc 30 10 40
dd 30 10 40
ee 30 20 50
ss1 20 30 50
ss2 10 30 40
So everyone gets a full 40, you can tweak it so everyone get 45.
Chances are, injury and fitness means that some people will player closer to 50 while others play closer to 30.
EDIT: As I said, this was done v briefly when we first had the idea suggested by Rocker (to see if it was feasible)