i had the same problem with a pair of my pants...
what i did was add side panels!
1.) Find out the width of your pants by measuring or looking at the label
2) measure your own waist/hips and subtract the measurement of the pants from your hips measurement. divide that number by two then at 3/4" seam allowance. this will be the width of your patchesat the top of the pants
3) turn your pants inside out
4) beginning at the bottom cuff, cut up one side of the outer leg seam, including cutting through the waistband entirely, then go up the other side of the seam and dispose of that. do it to both legs (be sure to cut off the metal grommets at the pockets to avoid breaking a needle_
5) decide how wide you want your patches to be in the leg. add seam allowance (3/4") and that is the dimensions of your patches. later you will trim the sidess so that is at the right width for the waist
6) start cutting out patches with the above dimensions, you can figure out how many patchies you will need ofr each leg by divding the length from the waist to cuff by the size of your patchies.
7) sew your patches together in a strip long enough to run the entire length of your pants
take the dimensions from the top of your patchies in the waistband and mark this at the top of your panel of patchies. from the bottom corners upward, trim off the excess
9) one one end, turn under about 1/2" and stitch, this end will be the bottom cuff for your side panels
10) with right sides together, line up the edge of the panel with the edge of the pants and stitch all the way up but stop just before you get to the waistband
11)again starting at the cuff, stitch up the other side of the patch panel, but stop before the waistband
12) fold over the top of the patchy panel until it lines up with the top of the waistband and stitch across, then finish stitching up the sides of the panel and reinforce by sititvhing back and forth in reverse at the top of these seams.
repeat 9-12 for the other leg....
13) try on your new patchy sidepanels and dance around!