I also suggest sewing it. You can just pinch it, and sew it, totally easy..... and then it's totally easy to cut the sewed part out when you need too.
~I have 2 tall skinny sons (they have their daddy's long legs)and I LOVE the adjustable waist pants, whomever came up with that idea is a genius! I also make sure that his PE pants (as I call them) have drawstrings that can be tied!
My oldest tall son is now 18 and wears a 32in waist & 34in length, thank goodness for Levi's!!!
My 2nd tall son is 9 and could fit into a size 7 waist but needs a size 10 for length! Argh! Once again, thank goodness for Levi's...I am in love with Levi's 514 for the lil' guys, they are so cute and they have the waist and length sizes just like grown-up Levi's!!
-----After you edit-----------------
You don't need sewing skills to sew up some PE pants. You can tie a knot right? Thread the needle, pull the thread through and match up the 2 sides of the thread so they are the same length, tie a knot at the end and then push the needle through the inside of pants (the only important part is to make sure you start from the inside) pull it tight and then go back through a couple times...it only takes a few stitches. I have done this a million times...it's totally easy! You can do it, promise!