leadegroot - 11:24 am on Aug 10, 2011 (gmt 0)
A different suggestion:
When http://www.example.com/widgets/round-widgets/blue-widgets is out of stock.
show the content from, say,
and add a canonical tag to that blue-widgets page.
Google sees that the correct page to show is the other and you don't get a dupe report.
I am doing this on one of my sites (not e-commerce, but I have entries that pop in and out and I don't know if they will return) and am watching to see what the effect of removing the canonical is when (if) the entry returns.