A few ways Ive done it.
Ball turning tool works very well concave and convex shaping. I use that method most. You can also cut the basic shape with the lathe in steps. Once you have the basic shape, use a half round file to contour your shape, then smooth out starting with 40 grit sand paper, going progresively finer.
The way I did the first couple of handles , though the slowest of all methods, is a coarse half round file with the lathe turning slow. You will need to play with the speed to find the sweet spot but does just as nice of job. You would be surprized how quick you can shape a handle with just a file.
The other way Ive done it , is mount your tool bit with it inline with you compound bolt. Loosen the compound enough to swing it, and will save some time too. You will need to have a 4-way turret tool post to do this.
Usually these type of handles are threaded on the end. Your best to take care of the end threading first. Other wise grabbing the handle later will be a big problem.
I have at times turned the stock for the thread, and either single point , or use a die, and get that outta the way first. But now its got a threaded end, how do you hold it to work on? Just head to the scrap bin, get a piece of round stock, drill and tap for the thread on your handle. This scrap piece, will also be used to get your work piece away from the chuck at a safe working distance.
This helps if your using a ball turner, swinging the compound, or free handing it with a coarse half round file. Ive found that to get the handles to look the way I want, I do a certain amount of free hand file work at the end of machining. Switch to a fine half round for the finishing shape. Then the sand paper starting with coarse, moving up to fine.
So, if you have little to work with, you can still make a nice handle with your lathe and just a file! Some handles are shaped like the end of a baseball bat, others shaped like a candle flame, both styles can be done with files. On a final note, when working around a spinning chuck with a file, make sure the file has a handle on it, not the pointy bare end. And be very carefull when filing on the lathe. Stand off to the side slightly, dont put your body in line with the file.