I JUST saw something about this in a tutorial video for MC6T yesterday. I upgraded from MC6 and was just making sure I saw any hidden features which might be of interest.
This one did interest me, although I don't know that it was new in the upgraded product, as much as that I hadn't known of it before. Basically, you set a default note type/length for anything you "write" into a midi track. I'll try and find the video and let you know what it says to do.
However, it is possible this won't work quite right for importing something, since you don't want to change note durations. The other way I'd recommend, which is sure to work, is to select everything in the midi clip and then just drag the length of one note out a small amount. If you quantize to 1/16 or 1/8, it should remain workable, and then when you're done editing, you can just pull them back that 1/16 or 1/8.
I realize the second option is not very sexy and certainly still requires some work, but I thought I'd put it out there. I'll check on that preset midi note thing and see how it applies to imported tracks (dragged in, etc.).