First you can not put any WA lens on the Panasonic adapter...You need an aftermarket adapter.
And the DCR6600 is a very good WA lens but on the FZ20 there is a bit of vignetting in each corner, which can be cloned out but if he does not like to PP maybe you should look at a different lens.
While not as wide or as good the DCR720 or 730 should work as the WCon 07 or 08. Also the Raynor HD7000 is a pretty good lens. But do not forget you need an aftermarket adapter with any of them.
To maybe simplify thing if you were to send Lovelife a PM or an Email he could fix you up with an adapter and lens and his prices are very competitive.
Here is a link to some stuff he sells and you can contact him there also.
Click on the CRING adapter and see if you can follow from there but its more than a little confusing which is why I suggest contacting him.
http://search.ebay.com/_W0QQsassZjkQ2dconsultants