release strategy & EBAN for project systems, purchasing

Hi

We have 2 different scenarios for which we use same account assignment category "Z".

1) Purchase Requisitions for capital expenses (Account assignment category "Z") - this is part of project systems requisition attached to WBS elements

2) Purchase Requisitions for expensed items (Account assignment category "Z")

I have configured release strategy with classification with following characteristics

1) plant

2) cost centers

3) total amount in PR

4) account assignment category

all 4 characteristics are same in both areas (capital and expensed)of purchase requisitions, account assignment category Z decides whether it is capital purchase or expense related purchases. Z uses order number that is internally tied to WBS element.

my question is - if some one has similar scenario then what is the best solution to handle invocation of release strategy.

how release strategy can be determine, do I need to use user exit and if yes what best user exit is available.

EBAN fields, I have researched and I cant use fields like "requisitioner" for determining release strategy.

I would like to invoke different release strategy for capital projects and different release strategy for expensed items in PR. there is a workflow attached to this later.

Please reply

Thanks and regards

Umesh