I think it should work if you set target and stop always directly after opening a position. When cumulating is activated PRT obviously takes the set target and stop only for the last addition to the cumulated position.

Then I see no possibility to influence this stops or targets for the different parts of a cumulated order. You always can only manipulate the stop and target for the last part that you opened at tradeindex(1). So one can set this stops and targets and leave them in the market and can have an additional SL for the whole position (or what is left).