How can I mend leather boot lining?

I have a pair of Frye boots with leather lining. The lining in one boot is ripped so my foot gets caught when putting them on. If I force my foot into the boot, the lining will rip further. I took it to a shoe repair shop, but they couldn't repair the leather lining. I love these boots and they are still in great shape otherwise. Should I try to adhere the leather lining to the outer boot with glue? Is there a safe product that would keep the leather soft and pliable and that wouldn't bleed through to the outside or damage the boot?