Dunno about "true anamorphic." But I have shot with a anamorphic adaptor & squeeze mode (until I got my lense scratched.) What I did was simply set the anamorphic adaptor flag to true (I use FCP may differ for other programs.) and then I went into the motion tab under distort/aspect ration and set it to -33.33
Looks pretty good most of the time, if you didn't get good focus, then it may be blurry. Thing is squeeze mode footage with black bars look better than the squeeze+anamorphic. The only real advantages with this setup (anamorphic+squeeze) are apparent when you have really wide-static (tripod) shots.
Having not used the anamorphic adaptor in a while I've found it to be a lot less troublesome for run-and-gun situations.