I just picked up a Track Spare +. A polyester ball like the Window Spare. At box finish and polished up it will go straight. Change the surface to suit your needs and you'll take the straight right out of it unless you roll it dead flat.
I'm loving my track spare +. 500 was too much. Now I keep it at 1000 or 2000 depending on what I'm seeing. When the heads and mid lane get burnt or tight and all else fails I can grab the spare +, move back right and crank it straight up between the 1and 2 arrow and keep the pocket. Entry angle isn't that strong so carry is an issue, but it will keep you out of trouble.