One of our cats is diabetic, the other has chronic constipation. I very much doubt massage will have a significant effect on the constipation. There are many ways of treating this, depending on the cause. Does your cat have megacolon? Is there an underlying condition causing the constipation? Are you dealing with a motility problem, and perhaps need medication for the motility?
Just remember that, the longer the stool remains inside the intestine, the harder it becomes, because the intestines will continue absorbing moisture from the poop. The harder the stool becomes, the more difficult it becomes to move. It's a vicious cycle. SQ fluids really do seem to help, but need to be used in conjunction with stool softeners (e.g. Miralax / Kristalose / polyethylene glycol) and, often, in conjunction with motility aids as well (e.g. Cisapride). There is also lubiprostone, which is both a motility agent and stool softener in one.
However, if the constipation is very severe, starting to use a motility agent without first clearing out the blockage (e.g. enema) could cause further problems, not to mention severe pain.
Getting enough liquid into your kitty is half the battle. Wet food is best and SQ fluids are amazing.
