How do I stretch new riding boots?

I just bought a pair of Saxon Equileather Boots in size 10, extra wide calf. I went to the nearest Dover Saddlery store about 30mins away and tried on a 10 regular, and the employee said that an extra wide calf should fit me just fine with a comfortable amount of room for jodphurs and breeches underneath the boot....anyways to the main subject of this....so i put the boots on with my Ariat boot socks and what do i discover...the zipper goes up like 65% of my calf and WON'T BUDGE...i'm tallking a jet airplane could not pull up the zipper. Extra wide is the biggest calf made in any type of riding boot Ariat, Dublin, TuffRider, Cadence (discluding custom made boots)....how do i scretch the leather where it goes around my calf completely? the boots fit fine in the foot, ankle...it's just at that one spot on my calves that the zipper won't go over. i most likely will start showing in september, and i really don't want to have to get paddock boots because i'm not a fan of them, and when i purchase half chaps for them, i'll just have the same problem all over again because my calves are huge from being in marching band, and im also a somewhat plus sized rider. i don't want to purchase custom boots because i'm on a tight budget and they're like $800.