My 13-year-old was diagnosed diabetic last January.  The vet taught
me to inject him, but didn't think it was necessary to home test him,
and wanted me to inject him with 1 unit twice a day.  I was relieved
to see, when the vet taught me, that he didn't notice he was being
injected.

Fortunately, I disagreed about the testing, and started testing him
the day after he got home (the vet kept him for 4 days).

After being switched to low-carb canned food (initially Science Diet
kitten food was recommended by the vet), he tested in normal range
without insulin.  I tested him twice a day before feeding for three
weeks, and then dropped to spot checks a couple of times a month,
along with keeping an eye on the daily water dish levels and his
output in the litter box.

At first they thought it was a treat, but both cats started refusing
the Science Diet kitten food after a couple of weeks.  I switched
to Iams kitten food, which they liked for a couple of weeks and then
refused.  I then sought out a local Wellness dealer, and they've been
on the poultry and poultry-and-fish flavors of that ever since.
(I avoid beef flavors, because both cats have always barfed them
right up.  But, I've never seen a cat take down a cow, anyway.)

The ear stick is more frightening to think about than to do.  My cat
is a little annoyed with having his ear held and warmed before the
ear stick, but doesn't notice the prick at all.  I've tested my
non-diabetic cat a few times (who, btw is a Maine coon), and he
doesn't notice it either.

You might want to smear a tiny dab of vaseline on the edge of his
ear, so that the blood beads up better above the fur.  You'll want
to shine a small flashlight through his ear, to familiarize yourself
with where the vein along the edge is, so you'll know where to aim.

I use BD Ultra-Fine lancets, just held in my fingers, because it's
too hard to get close to the ear vein with any of the aiming devices.

I use a thin sock with about 3/4 cup of rice in the toe, knotted off,
and warmed about 10 seconds in the microwave as an ear warmer.  I put
a clean tissue over it before I put it in the inside of his ear, and
hold his ear on it with my thumb (while scratching his favorite spots)
until it feels warm.  The tissue is because sometimes you might go
all the way through the ear, which, quite frankly, is not a problem
compared to not pricking hard enough and having to stick him again.

For constipation, you might see if he likes canned pumpkin.  My
diabetic cat loves it, but the other doesn't have much interest in
it.  It has lots of fiber, but very low in carbs and calories.

Home Testing of Blood Glucose for Diabetic Cats
By Margie Scherk DVM, ABVP
 (home testing movie, Windows Media or Realplayer)
  http://www.veterinarypartner.com/content.plx?P=A&S=O&C=O&A=605

Harry's Home Testing Page - (good close-up photos)
 http://www.sugarcats.net/sites/harry/bgtest.htm

Punkin's Home Testing Movie -
http://tlb.best.vwh.net/bg_punkin/test_bg.html

Feline Diabetes
http://www.felinediabetes.com/index.html

Pet Diabetes
http://www.petdiabetes.org/

Frugal Feline Diabetes site
http://www.sugarcats.net/sites/jmpeerson/frugal.html
protein/fat/carb counts of canned and dry foods.
http://www.sugarcats.net/sites/jmpeerson/canfood.html
http://www.sugarcats.net/sites/jmpeerson/dryfood.html

DVM the Newsmagazine of Veterinary Medicine
 At Home Diabetes Management -
 http://www.dvmnewsmagazine.com/dvm/article/articleDetail.jsp?id=13315
 
 Blood Glucose Monitoring -
 http://www.dvmnewsmagazine.com/dvm/article/articleDetail.jsp?id=5336

VSPN discussion on Home Testing -
http://www.vspn.org/Library/Rounds/VSPN_LC011209.htm