How do you plug an unwanted brake line?

[aerosam]

Hi Guys,

I'm using my donor's master cylinder, it has 2 outlets, and used to feed to an ABS controller. As I'm not using ABS, and my rear discs are actually bigger tha my fronts (for now) what i want to do is just use one port, and fit a knob type brake balance valve to reduce pressure to the rears. So how do I blank off the other port securely?

BTW, I'm aware the balance vale is a fail on IVA but I'm building this car purely for the track so it's not a problem.