As you can see, I live in z4 also. I plant the sweet potatoe vine every summer in a huge pot out front. I also like to plant morning glories on the side of my front porch. For me, the morning glory is at it's best in August. I wish it's season was longer as I love them but not in southern SD. Whereas, my potatoe vine has been growing all summer. Maybe if you start your mg vine indoors so it can be well established before transplanting it, you could have them at the same time. My mg vines are much thinner and more fragile than the sp vines. I love them both but have not actually tried them on the same trellis. I have also mixed the mg vine with the cup and saucer vine. They are both late summer vines for me. Well, have fun experimenting.

I never knew that sweet potato could grow up vine. I've only ever seen then used as trailing plants.

But maryz4 is right you could start your MG indoors early and get them a leg up.