Hi Allen. Solo is easy, its just a technique to learn.
Put on the base pack. For stacking (or as I say, for a T-up), lay the pack to be T'd up in front of you, sideways. Grab each end of the shoulder strap closest to you with each hand. In one smooth arcing motion, and fast so that the momentum of the pack carries it to the top, pull the pack around to the one side high, and then just let the arc continue until it rests sideways behind your head, across the base pack. If you get the arc right, the pack will "want" to settle right behind your head on top of the other pack. Do not cross your arms. If you cross your arms it won't work. Keep the arms parallel and just heave up with that smooth arc motion. Use physics to swing that arc way out and up, and that pack will almost finish the move on its own. Its not a difficult strength move. Practice with a light pack and you will get it for life. Then its just muscle memory.
You will likely find you do it the same way on one side every time. I always arc up the T'd pack lift to the right. As others have mentioned you can use the shoulder strap as a light tump, which is what I do, and it keeps it from sliding off. The pack shoulder strap you grabbed closest to you will now be the closest one to your head, so the control is never out of your hands.
Some guys do a straight flip over their head of the T'd pack. I find that method is too hard and jarring for me, and if it fails, its hard on the back catching the falling pack. I like the graceful arc swing to the right and up for a smooth pack landing.