"Beg" trick

I'm trying to teach Tynan the "beg" trick. Maybe I should have thought of teaching him this one when he didn't weigh so much

Any pointers on how to teach him this trick without throwing out my back?

Just so I'm sure... which beg trick do you mean. The sit up and beg trick, the dog prayer beg trick, or the drool on your leg while you're eating beg trick?

the one where the dog sits back on it's haunches and hold up their paws.

I've always just lured it - start with the dog in a sit, hold a treat just barely above his nose, and lure it backwards toward his tail until even one foot comes off the ground. Click the foot coming up. Continue this way until he's lifting both feet, then holding the position for longer and longer.

It's physically a difficult behavior for a lot of dogs, because it requires them to use a lot of muscles they don't normally use. So take it slow in the beginning and practice it often to keep his conditioning up.