Bands march in 5/4 and 3/4 all the time. LRL, RLRL then RLR, LRLR. Set the drill times in blocks of 3 + 4 and/or 3 + 4 + 3 + 4 counts - 14, 21, 28, not the traditional 16 or multiple of 8. You're just doing multiples of 7 instead.

Have a good drill writer who understands this.