You could just take some hockey tape and wrap a straight line around the shaft and cut to that.
This --^
If the hack saw's steel is like most, it won't last long. Instead, I use one of these:
https://www.homedepo...0547L/202710512 and adjust it to be a triangle instead of its default rectangular shape (creates more tension on the blade and prevents it from bending).
And then bought replacements blades (most hacksaws are made for wood/plastics, not carbon fiber, so after about 5-10 sticks, you'll want to replace them):
https://www.homedepo...20558/205049947
To expand on Moose's suggestion:
1. Start by adding a piece of tape around the body.
2. Place the body on a flat surface with the head of the body hanging over. (I use my bed -- it works well enough).
3. Place something heavy on top of it to weigh it down. It shouldn't move without quite a bit of force.
4. Hold the head with your non-dominant hand, then place your saw blade against the tape, then very lightly score the body. When scored, apply some light downward pressure. You shouldn't need much pressure to cut through the body's sidewall. You need to allow the saw blade to do most of the work. Don't force it and take your time.
5. At some point the saw blade will stick, no longer cut, may flex and move the body around. Stop!
6. Flip the body to the next uncut side. Part of this side should have a small cut-line from the previous cut. Use that and the tape as a guide. Lightly score the body and then begin cutting again.
7. Rinse and repeat until you've cut through all 4 body sides.
8. Finish off the freshly cut edges with a filer.
9. Take a wet paper towel and wipe down the outside and 1-2" inside of the body.
10. Take a dry paper towel and clean off any residual fragments.
Note: Attempting to cut through the body in one go will require too much downward pressure and will bend the saw and give you a crooked cut. Again, allow the saw to do most of the work. If it sticks while cutting, flip the body over to the next side. The basic idea is to individually cut into all 4 body sidewalls with the same pressure while using the tape as a guide.
Total cost: $30