How to do it is the question.
1. Cat lives here. I'm not keen about blocking on a low horizontal surface where he can have a heyday on it.
2. It's big. I'm afraid our double bed is not large enough, nor is any floor space we have even if Cat did not have a proclivity to resting on knits. Even if it did fit on the bed, I doubt the worsted weight yarn would dry in time for us to be able to use the bed again.
3. It needs tension. Right now it looks like a saggy breast when held up.
My thought is to build an octagonal PVC blocking frame using 3/4" pipes with a 7-foot diameter. If I'm thinking correctly, I'd need one 4-way join for the center supports, four T joints, and eight 45-degree joints.
Using a nifty Octagon Layout Calculator I found online ( http://www.pagetutor.com/octagon_layout/ ), I figured out that if each of the octagonal sides were 3 feet long, the diameter would be about 7 feet and 3 inches. Good enough, I say. Then it's a matter of cutting the cross pieces into roughly 3.5-foot segments and fitting everything together with the joints. Cutting is probably the trickiest bit here.
Is that sounding decent? It's been a long time since I played with Legos. Or is there perhaps a better solution for a blocking frame I haven't thought of? I'm not interested in breaking out nails and wood; I attempted carpentry in a past life and was kindly discouraged from continuing with my efforts. Plus I like the thought that I can break down and reassemble the frame as needed without fancy tools, once I've hacksawed everything to the right lengths.