say u left architecture cos the monotonous drafting had burned your soul, that you tried to express this loss of self thru a career as a performance artist but found out that u had no talent, but am now ready to go back to kissing ass in an un-fufilling, middle-of-the-road firm to pay your by now large debts.

I left for awhile, then came back, interviewed in a variety of firms, was asked that question 3 or 4 times, and always answered briefly (1 or 2 sentences max) that I took some time to work on a project outside architecture, or that I was exploring other options, and that now I had made the choice to continue on in architecture. This was always met with an "ok", "I see", or a nod of the head, with no follow-up questions, and I was always successful in getting an offer.
I wouldn't worry about this issue too much. It's not likely to be a big problem unless you dwell on it too much yourself in the interview.

Your diversion may allow you to stand-out among other candidates who have only worked for architecture firms. Try to focus on the positive aspects of your experience and how they have enriched your understanding and perspective of architecture.

You could say you gave porn a shot.

i can see it now tyvek...

interviewer: i see you have not been working in the field of architecture for the past two years.

tyvek:that is correct

interviewer: what field have you been working in?

tyvek: the entertainment business. i was an actor.

interviewer: really, that is quite interesting. have you been in any movies?

tyvek: yes, i was in boner jams '03, flogging for a logging, what's filling Gilberta's grape and i had a cameo on "the office". have you seen my work?

interviewer: i thought you looked familiar, you were excellent in boner jams '03...your hired.

"Now let's go erect, some buildings, tyvek. Har har har har."

"Indeed... boss. Har har har har."

"and what brings you back to architecture?"

"Groin vaults, baby. . .nothing but Groin Vaults!"