I have.
I nailed nails into the outside of the W.box and ran string from the nails up to the eaves of my porch for them to climb.
I suppose they could be left to cascade down, but they like to grow upward, so not sure what they would do, but I bet they would be gorgeous.
I LOVE Heavenly Blue MGs. The most perfect color of blue.

That's what I'm wondering if they will cascade or not. I did plan to put up a short white trellis in the box towards the back to let them grow upwards to give a look with a little more height. The only thing is I also am concerned that the plants wont' be happy in that shallow window box. Then again I know what monsters they can become. They might go right in between the old siding boards on the house.

Decided there was no need to soak the seed esp. when I'm still deciding whether to sow them! lol I'm going to think about it some more.

We grow them in large pots every year, here's what they looked like early summer 2 years ago. They actually got so long they covered most of the deck railing by the end of summer and were enormously bushy. We actually planted them in Miracle Grow Moisture Retaining potting soil just because that's what Sam's had and it was pretty cheap, the MGs didn't seem to mind at all....

My experience has been that they grow up. I could never get them to cascade.

Skibby