Is it possible to have two way permalinks?

Hi,

i have a question on permalinks. Currently i am using the folloing structure for my site:

/%year%/%monthnum%/%postname%/

But now i need

/%postname%/

cause i am using wp as a cms system. But there are many sites which are linking to my pages through the above (/%year%/%monthnum%/%postname%/) structure.

Is it possible to use both ways in one installation?

regards
yavuz