Hm, If you really, really want to make sandals, here's how I would do it:
The leather only connecting to the sole at two points makes me worry about stress. I'd have at least two more attachment points on each shoe.
I'd also cut some holes in the back so your ankle doesn't overheat ; )
You also might try getting them stretched, but this will probably not affect the shoes at all, seeing as how it's pretty tough leather, and it could damage the boots. They'll charge you even if they know it won't work.