permalinks with and without categoryname

Hi,

I want access my post links with and without category name in permalinks.

eg
http://blogs.mysite.com/hello-world

http://blogs.mysite.com/announcement/hello-world

as of now my permalink loads without category name in it. when I add %category% in my permalink setting, old link is not working. is there any workaround to access both links ?

Cheers,
Fred