Custom Polymeter?

I’m inputting a reduction of an orchestral score with simultaneous 6/8 and 3/2, where one bar of 3/2 is equal to three bars of 6/8. Inputting a meter of 3/2 in one line goes to the default of it equalling two 6/8 bars. Is there a workaround to achieve this?

Yes you with a little workaround. On the staff where you want the 6/8 enter “6/8,4” into the popover (and press alt-enter of course). Then, on the second measure of that staff, invoke the shift-M popover again and enter either 2/4 or 1/2 with alt-enter again. Hide the 1/2 and then enter a triplet for the first beat of the second bar. Copy and paste the triplet for the duration of the passage (you can even select one or two bars’ worth and type “r” for repeat), create a 6:4 tuplet for the 1st measure and enter your music. Here’s what it looks like (without the first bar tuplet …):