I suppose this is the best there is:
*.shang sub .setaim store
*.maxvel .up store
You probably want to use *.shang - .setaim store
That is, sub is a binary command, so it's going to pull two values from teh stack. If there's only one, it'll get a 0 value, and do what you expect, but if there's still a number on the stack for whatever reason it won't do what you expect. The - command is a unary command, and negates the top value of the stack.
See the wiki page on
negate for more (well, not really
) details.