Obviously these may or not work depending on your seniority but here are a few ideas you may want to research once the bidding window opens. I don't have PBS access now but there are a few ways to do it:

The best way is probably to set condition "Minimum Credit."

If you are senior enough to bid for specific trips you can pick the trips you want (or enough generic trips to barely get you above the Line Construction Window minimum) and then bid "avoid trips that credit > 0."

This will prevent PBS from putting additional trips on your line after you reached the minimum line credit.

Either of the above will try to build you a minimum credit line. You then have to insert something that will start a reserve bid group if your bids are not honored.

I have had good luck with the "Else start next Bid Group." I think there might be some other ways to this but I don't recall the specific commands.

Anyway with the above in mind review the PBS bidding gouge or call the PBS bid assist guys once they are available. You can also search Youtube for some of the PBS Bid Assist videos.

Good Luck - Scoop