I dunno. Usually you work it the other way...start small (on the gravity) and build up to a big brew on the last pitching.
How 'big' was your Tripple? it might be ok, or it might not. if 1214 is a belgian yeast it might throw a lot of phenolics into the fat tire clone (which may or may not be pleasing).
i agree with malkore, the phenolics may be odd in a FT clone. with cheap yeast like safale 05 and nottingham available, i'd probably just use one of those.
+1 on phenolics. Belgians are known for it. I don't think it would be to style at all. On the other hand if you were to ferment cold enough without stalling it would keep most of the phenolic at bay(maybe). I would wash and save the yeast and use 05 for this brew.
fat tire is not a belgian beer and doesn't have the esters and phenolics that you're going to get from either of those yeasts. I think for a clone you'd be best off with something very clean like 001/1056/S-05.