I'm 99% sure that it has been done on here before, but I'd not seen it in this challenge , and I did actually knock this together myself rather than rip an existing one off collegehumor...
Which is a long-winded and quite self-deprecating way of saying - cheers!
(
barryheadwound Mul-ti-pass? Multipass!,
Fri 1 Nov 2013, 12:48,
archived)