While Labor Day (the specific weekend) will be a bit difficult ... use the EF feature (have you found it yet) to do the +/- days (up to three days)?

I wanted to do some Christmas shopping over the US Thanksgiving weekend in Europe .. and found flying on Wed/Sun was hard for C class availability. With the +/- feature found LOADS of availability on Thursday and Monday. So I take an extra day off from work .. and eat airline food instead of family turkey .. I got confirmed upgrades! At the time of booking!

Good luck with your Labor Day runs. Be aware that C availability FAR in advance (and perhaps on a non-business travel weekend like Labor Day) also may be impacted by the 'new' Yield Management feature.. where they have to sell one business class seat (it appears) in order for any C to open up. C0 and an EMPTY seat map means no one has popped for a J fare . and the C will not open up. Kinda a bummer on trying to plan for Thanksgiving/Christmas/Halloween trips.