Its no problem and commonly done in the northern plains for spring wheat burndown (2,4-D ester + Glyphosate), even up to emergence.  Others in the southern plains and midwest have reported problems using 2,4-D ahead of seeding winter wheat.  Would a generic SU like nimble fit your weed spectrum?

Edit to add: 2-3 oz of dicamba has been safe here (ND) and may also be an option.