Believe it or not, I found a way that works, but it's frustrating at times. 1) Position the item you want geomerged exactly how you want it, but above where you want it. 2) Brace with single walls. 3) Leave a gap in the top to see the item. 4) Push down, hold on, save. 5) When you come back, it should be kind of lowered. 6) Adjust braces, save. 7) Push, hold, save. 8) Repeat.
you need to partially intolock wall into the object you want to merge brace it in and then you just tap A on the object and then tap A again if you want me to theach you send me a freind request gt=d4rkdemon
Um... guys the very edges of the double walls auto interlock very slightly, kinda like doors do on other maps, might try using them.