Everyone has their own opinion on this matter and that's fine. However, in your case, the size difference between the 2 snakes makes this not a very good idea.
Like SmoothScales said so eloquently in is post yesterday:
Originally Posted by SmoothScales
The reality of it is it's 'fine' right up until its not, and by the time its not it's to late and now you've got a much bigger problem on your hands. Besides - what humans perceive as 'fine' in our terms is not 'fine' in snake terms.
Thomas "Slim" Whitman
Never Met A Ball Python I Didn't Like