How to cable TT?
 

I have a bike with a curvy top tube (like below)
I was wondering if you would put ferrules on the brake line and have it housing less for part of its trip along the top tube or would you leave it in housing and attach the housing to the top tube in like 3 place to keep it running along the tube?
http://www.dodgecitycycles.com/wp-co...Bike_Whole.jpg

Run full length cable and housing, You can secure to the TT with zip ties.

Running along a curved tube with no housing isn't an option. The cable will automatically take up a straight line between the two brazed on or clamped on housing stops.

Some of the fancier frames of this cruiser style bike have oval holes or fillets with holes to allow you to feed the housings through the inside of the tubes for much of the run. Now THOSE look slick.

Something like these jagwire cable guides will ensure that the full housing doesnt move around too much.

Yep - they work perfectly. You can even find them in different colors to suit you. Put a little Teflon-based oil on a rag/paper-towel and pull the cable across a few times. You'll be fine.

I've seen esposed cable runs along the sides of curved top tubes before. You could do a 12" or so run along the side of the top tube with clamp-on cable stops.

I think I'd just run full housing, myself, though. I think you'd have to drop about $30 on cable stops and they ain't too pretty.

edit: one thing I didn't think about is that on the curved TT bikes with cablestops up there, the stops are brazed on so that the cable run is a straight line. If you use clamp on stops, the ferrules will be aligned on two different tangents, which would not be the ideal orientation.