Thanks for posting!
When I first started with Scrum, I was a developer and the SM like you describe, and this is a challenge.
We have this concept in the USA of "wearing many hats"...See more here on that: http://idioms.thefreedictionary.com...an+one+hat
When played a dual role, I would say stuff like "With my Scrum Master hat on, I would say <SM view on the topic>"... "On the other hand, with my Development Team Member hat on, I would say <Developer view on the topic>". Whenever there was confusion, I would use this technique. I would also use hand motions to mime putting a hat on to help convey the metaphor.
Ever since that experience, I have used this technique to coach SM's and PO's and even Managers on how to describe which role they are "speaking as".
Would this work in your context?