Whats the best and cheapest way to extend length of pull?

I have a Marlin XL7 (synthetic stock).

I looked online for butt pads, but did not find any for this gun and I don't know if I could make up the 2" or so that I need. It already has a decent sized butt pad.

Is it hard to lengthen a synthetic stock without making it look like crap?

How much would it cost to have a gunsmith do something?

Thanks!