Sounds like a dream come true to have a nice spotter as a lens and the quality of a larger APS-C sized sensor to capture the image. However I never wound up using my spotter nor my DSLR together. The ergonomics just seem to kludgy, particularly if you're traipsing about the wilderness with a tripod, spotter, and DSLR and attempting to assemble it all together in hopes that the big buck doesn't run over the hill. I'm in the same boat as you with an angled spotter. I don't think any of the wildlife pros on here shoot through a spotter so I hope they'll chime in if I'm wrong.
have you considered a third party adapter and buying a $80 pocket digicam? You'll lose out on some image quality, particularly in low light, but it might be a lot easy to maneuver and assemble in the moment of truth than your T5i.
Swaro's adapter is 450 bucks.
