I know lot's of people have done kegerators directly below their towers... Is flexible really needed? Perhaps a diagram to see what you're thinking?
Also, doing a black-iron pipe, make sure to insulate inside properly so you aren't just using it as a heat sync for the outside air into your freezer.
Finally, be careful going out the side... I almost did this, but decided against it because there are often coils on the sides of the units that you risk puncturing if you're not really careful. Wife was already skeptical on the whole project - she keeps saying I have really bad project creep ($$) so side ported scared me off.