Wouldn't mind compulsory work experience, but there are problems with it now;
The JSA is not a minimum wage, and certainly not based on the hours done by these workers;
The government pays these companies for this out of tax funds,
They displace paid workers, and a large employer can just keep a 'merry-go-round' of placement staff to cut costs.
There is no formal development of skills, just vague notions of "teaches them how to get out of bed and look smart herp derp". Funnily, they arent so keen on them learning the vital skill of receiving the correct pay.
I think that it would be better for the economy, to suggest to the unemployed skills that are in short supply, and train them appropriately so they can do this work.