An unpowered SCART block might pass through progressive signals via a component>SCART adapter and back out through a SCART>component adapter. The thing is a switch and you're just passing electricity. The question is will the quality of the circuitry be good enough to pass the ultra high frequency video signal for Prog Scan without making it too noisy to be usable? Seems like a very roundabout way to achieve what you want.
I suspect it would work but won't look as good as a direct connection or an AV amp with component switching - or a component switch like this...
http://www.joytech.co.uk/products.ph...lang=1&catID=9
A powered/amplified switch is probably going to find the prog scan signal too much to amplify cleanly and I doubt it would work at all.