Level42, do you mean like:
In Mame you can do this by making Mame accept only the diagonal directions. Here is an example for qbert:
Hit "Tab" and go down to "Input (this game)"
Go down to P1 Right and hit "Enter"
Now hit the down arrow then right after that hit the right arrow (it should say "Down Arrow Right Arrow" in just a couple seconds)
Now do the same for the other directions but use:
P1 Left: Left Arrow Up Arrow
P1 Up: Up Arrow Right Arrow
P1 Down: Down Arrow Left Arrow
If you make a mistake, just select the line again and press "ESC" to reset the control to its normal key.
Once you have done this, qbert is tons of fun with an 8-way stick!
I just tried this, and it doesn't seem quite right. Are you sure you have the correct values listed (P1 Down: Down Arrow Left Arrow etc...)?