Nev wanted to bob out his new stock V-star 250, and started with the exhaust. We used a Biltwell Builder's Kit for this.
BEFORE

V-star 250 stock exhaust by KrankEngineering, on Flickr
AFTER

V-star 250 custom exhaust by KrankEngineering, on Flickr
I chopped up the stock rear cylinder pipe to get some bits I needed for the rear pot. There is very little room there, I guess that's why Yamaha take the standard exhaust back and down to the mufflers, rather than out to the side. I wanted to do "out to the side", for no good reason other than I thought it would look better.

Chopped stock exhaust by KrankEngineering, on Flickr
So I ended up cutting out some new flanges from 6mm plate, and using the chopped exhaust, made up a little 90" hook to get the rear cylinder fumes to go to the right side of the bike.

Rear cylinder pipe section by KrankEngineering, on Flickr
With a second flange on the right hook section, we can now bolt up on the right side of the bike. I had to chop the stock exhaust hanger that is welded to the frame to get it in there.

Rear cylinder adaptor flange by KrankEngineering, on Flickr
Can't remember where I stole this idea from, but it works great. Ron Covell suggests using hose clamps for this job, but for long straight sections I get better results doing this:

Pipe welding clamp by KrankEngineering, on Flickr
Needed some way to hang the pipe near the rear of the bike, so I made up a couple of hangers from 1.6mm, roughly formed into the diameter of the 1-3/4" pipe, with some M6 studs (ie M6 bolts with the heads cut off) plug welded from the back. Then I welded these on the back of the exhaust (see next pic)

Exhaust hangers by KrankEngineering, on Flickr
With a bit of 5x20mm flat bar from the rack, oxy to heat it, bend it, make up a small tab to pick up the pipe studs, weld 'em together, dress, paint, done.

Exhaust hanger bracker by KrankEngineering, on Flickr
This came out better than I hoped, makes the bike look heaps bigger, is plenty loud, and makes you laugh when you ride it. Job done.

Custom V-star 250 exhaust by KrankEngineering, on Flickr