Switch M to the highest resolution tick involved. So,
M / * BPM 120 2 7
Would get you 7/2 on 120. (edit: If 7/2 means “7 notes over 2 beats”)
If you want the polyrhythm, use temporal recursion with 2 scripts. Vis:
1: TR.P 1
DEL / * BPM 120 2 7: SCRIPT 1
2: TR.P 2
DEL / * BPM 120 2 5: SCRIPT 2
Note that these will probably skew in time due to rounding errors stacking up. You might want to find a common multiple and sync things up at that point.
M: DEL.CLR; SCRIPT 1; SCRIPT 2
I: M * BPM 120 35
Uh oh, 500 * 35 > 16384. So uh this might not be possible at 120 BPM. 130 and up will work, though.
Also, because the rounding error is going to result in ticks that are slightly too fast, the sync action is going to produce 2 trigger pulses unless TR.TIME is sufficiently large to mask the second trigger.