So here's Gray's Pretty Picture Book Wolf Head Thing For Moron's 101 - Jurnall In Pro-Grose.
This level.
See how this wolf is stuck in that crack? Its the same idea, but on a horizontal surface. I lost this wolf somewhere after he disappeared. I think he fell through the wall.
Yes, I used cheats, I'm playing on Insane, I'm lazy and I didn't feel like having to try harder than I had to, to beat three wolves on Insane (As a side note, power 9000 = exploding bodies...according to the wiki, power changes the amount of health you have...). Also, set the map to "mapgosomewhere" otherwise the level ends when you kill everyone.
This was accidental but its a perfect example of what I'm talking about. See how the wolf's head is stuck between both of the ice blocks? Exactly like that.
I finally got the wolf up to where I wanted, but I overshot, and trying to get it stuck from the other way doesn't work. You don't have enough control over the angle or the power to make it work, even with cheats. Too much power (anything above say, 0.4) and the wolf will fall off, too little power (anything below 0.3) and the wolf doesn't move.
So I went back to the pillar and managed to get his foot caught in between the intersecting ice blocks.
In conclusion, getting someone's head stuck in a vertical wall is possible under the right conditions, but the angle has to be right, you have to kick them in the groin so they fly head first into the wall and you have to have the right angle and amount of power (the default strength won't work, I was using a strength of about 1.5 for this whole thing)