It takes some work (and might take some time), but it IS possible. Here is how you can guarantee the pushwall does NOT move a third space:
1. Save your game before pressing the wall.
2. If you do not know how many cycles DOSBox is running in, or you have set it to run at max cycles, quit the game and type 'cycles' (without the quote). If you know how many cycles DOSBox is running in and it is NOT cycles=max, skip steps 3 and 4.
3. When you type 'cycles', if the string 'max' is returned, type the command 'cycles=x', except make x some number probably around 30000. If a numerical string is returned you do not have to do this.
4. Restart Wolfenstein/SoD and restore your saved game.
5. Switch to your knife (this is assuming CTRL is your fire button, so you waste no ammo). Hold down the CTRL key and press whatever key you use for the open door/press wall function. As soon as you have initiated the pushwall, press the F11 key rapidly (make sure CTRL is still held down).
6. Eventually after pressing the CTRL+F11 combination enough times, if cycles is not at 'max' (which we made sure in previous steps), the game should eventually start running very slowly. Watch for the movement of the pushwall to start looking very choppy/slow, rather than smooth. This has to happen before it has moved a full 2 spaces. If the wall starts to go a third space, restore and repeat the process.
7. Once the game is running very slowly and the wall hasn't already moved too far, stop hitting F11 and leave it running very slowly. The wall should stop only 2 spaces out!
8. Once you are completely sure the wall has stopped, now you just have to speed up the game again. If you hit F12 with CTRL held, this should start to happen. However, if you require cycles=max or want exactly a fixed number of cycles, then save, quite the game, and type the appropriate 'cycles=' command.
This can take a few tries the first time around, but once you're used to things on your particular computer the process should not take as long. Of course if you require cycles=max for normal running, this will take longer, since you have to quite twice (before and after handling the pushwall). But hey, at least there IS a solution!