In reply to Boulderdash86:
You could perhaps place bolts in the floor and support the line on A-frames/trestles. Otherwise you'll need to make some sort of frame and it'll need to be pretty sturdy (or clever).
A simple 2 triangle frame in 2x3 (or lighter with additional triangulation) plus a couple of brackets screwed to the walls (only loaded in shear so won't pull the wall down) to stop it buckling is the simplest structure I can think of. Basically a length of timber running wall to wall along the floor, a post stood up each end of it to attach the line and a pair of compression members running back to the mid point forming triangles to support the posts. A metal bracket or timber block fixed to the wall each end holds the posts down (but not in against the wall). As described you'd need to add some feet or modify the wall brackets to stop it falling over sideways but they don't have to be especially strong
jk