Can't speak for EZBid but I'm guessing you're speculation is correct. Nobody knows which trips will be "LCA" trips until the Captain bids are run.
It sounds like we're in similar situations, so my general strategy is as follows:
1. Prefer off dates I want off
2. Avoid anything I wouldn't want to do if I end up flying with the LCA, he calls in sick or I'm otherwise left flying the trip
3. AWARD trips if LCA - can make this layered, multiple lines if you want to preference trips within the LCA trips available at your seniority
4. Avoid anything else I don't want to do on a normal trip
5. Award trips in order of stuff I want - commutability, layovers, etc
6. Depending on how picky your requirements are you can clear Sked and restart another bid group but I generally do it all in one
7. If I'm sure I'll have a sked built by this point I usually finish with Avoid Trips if AVG Daily Credit > 0. This prevents PBS from tacking on some crap trip to get me to the threshold (PBS will not deny an avoid to reach the threshold, and this will leave your Sked alone as long as you've gotten at least to the bottom of the LCW)
Hope that helps someone and that you're actually junior
Otherwise disregard the above