First, it is a pain. I think the mobs have to be green to you for the pet to get any exp. One of the commen methods is spec Surv or MM and run instances with your pet by your side. If the pet is at least 60 you can probably send them into combat with out too much risk.
If you are going to level a cat, I know it is much further, but I suggest a ghost saber. If you have not seen one check it out. I have had my cat since lvl 32 and I am still tempted at times to swich. With the changes in wrath I will probably pick on up.
Which brings me to my 2nd point - if you can hold out a few months it will save you a little effort. In wrath pets will jump up to 5 lvls under you. There will be new pets for beast masters too - for example devilsaures will be available to BM hunters.