Activity weight

hi I have a problem in primavera

I need to put a weight for each activity

the weight is combined of resourses and cost

but I dont have any recorses or cost

in other word each activity have a specific weight so the hole project will be 100 %

I can add a field named weight but i need it to be changed with the persent complete

so if 50 percent of some activity that weighted 1.8
the remaining weight will be .9

and the perpous of the use of it is to calculate the money we should pay every month to the contractor

I know that look stupid you will tell me to define a resorces and there cost and we will have the cost

BUT

that how the boss wont it