A few suggestions (you'll get the idea), decide which pole you are going to use then
1 - Get a pen / marker top which fits the end of the pole and then tape the top to the rack at the height you want
2 - Get a piece of foam and insert the pole into it, then tape the foam to the rack.
If your going to remove the pole often then don't tape the bottom of the pole, if your going to leave it on all tour then tape over the bottom, tape or cable tie the top..
Carlos