If you are using an Ethernet Shield with a W5100 chip, this seems to be possible to do... however, there isn't any library method programmed yet to do it in the Ethernet library.
If you download the W5100 manual and move down to page 31, you can see that the register Sn_DIPR holds the Destination IP address that can be written when in client mode or read when in server mode.
It's weekend now, so I won't have time for this. But maybe on Monday I can put together a function to test this and share with you guys.