To accommodate the Revi C12B in the 109B, they needed to mold a wedge into the windshield to stop the gunsight from rattling against the windshield (From the 109B weapons manual, L.Dv. 228/1 (1937), page 29). On most 109A/Bs, they cut out part of the panel and glued on an outer panel. See:
http://www.moskittech.ru/eng/myze/Bf.../Bf-109B-1.htm photo #33. Later they simply changed the slope of the windshield from 45 degrees to 35 degrees.
So, there was very little spare room in that aircraft, and I side with those who have doubts about a gyro gunsight fitting into the cockpit. But, the Germans could do amazing things when they needed to, so nothing would surprise me.