Having looked into this myself, I must say that there is little to anything conclusive regarding whether a 6-position collapsible stock would, in itself, make a rifle violative of CT statutes. Likely, it would not.
However, per C.G.S. 53-202(a), a rifle with a detachable magazine (i.e. an AR-style rifle) will be deemed an "assault weapon" of it has "at least" (to be read as "two or more") features common to an AR-style rifle. Since "pistol grip" is included on the list, and imaginably on your AR, the addition of a collapsible stock would likely run afoul of the law.
Check it out yourself here:
http://www.cga.ct.gov/2005/pub/Chap943.htm#Sec53-202a.htm
Also keep in mind that the possession or control of parts that can be "rapidly assembled" into an illegal configuration is the same as having the assembled rifle in your possession.
Finally, C.G.S. 1-2z, the "plain meaning rule" is the law of the land in CT in terms of understanding how a statute should be read; trying to argue the engineering merits of a particular stock design (say, the "collapsibility" of a VLTOR design versus a true 6-position M4 style) would be an expensive legal exercise in how "plainly" the 'evil features' statute should be read.
In your situation not too long ago, I decided to go with a RRA Entry fixed stock in order to accomodate my need for a short-stock rifle. I also decided that I will be moving to New Hampshire or out west in May of 2009.
HTH