Using the same Volta (repeat ending) multiple times.

I have a piece in which the main verse and refrain section repeats 6 times, and I want the end of the refrain to slow down the final time. If I were doing this with a song that repeated once, I would merely set the normal ending of the refrain under the “Prima Volta” option, and set the slowed ending under the “Seconda Volta, open” option. However, because I am repeating the section 6 times I do not know how to do this properly. I have seen a repeat ending marked with, for example, 1-4 before, but in musescore there is only the option to mark it 1, 2, or 3. Any help would be appreciated, thank you!