Natalie, yes you can do this pruning. What will happen is after you nip the end of the vine, secondary vines will grow out from the leaf nodes. You will get more flowers by doing this pruning, actually.

Thanks Joseph! I was hoping that it would work. I've always noticed that the MG that I have planted have usually bloomed from about 4 feet up and above, instead of near the bottom, so I was afraid that I'd lose all blooms. I don't know why I've never tried it as a test, but I'm glad to hear that it will work!

I had wondered about that as well, but was too chicken to try. Nice to know it will work!