Well, I might approach it this way. You should be able to center the peep in the middle of it's adjustment range, then measure how high the center of the peep is above the centerline of the bore (i.e. center of the striker on a bolt action).
Then move out to the muzzle. You should be able to do some simple math and figure out how high the bottom of your front sight bases dovetail is above the bore. 1/2 barrel diameter at the muzzle + front sight base height. Now take the bore center/aperture center dimension, and subtract the frontsight base to bore height...following me?
Another way is to sandbag the rifle somewhere safe where you can look at a distant object through the bore, then cobble up anything, a toothpick in clay for instance, until it allows you to sight through the bore and through the sight at the same object. Measure your ersatz front sight, there's your front sight height.
