Er..yes!
That will work if you have no intention to use your 3500 as a link speaker as well.
Actually you need a ML Converter (type 1611), the Ipod will connect to the converter via a 3.5 mm jack to 5 pin DIN adaptor, and the 3500 will connect to the converter via its usual Masterlink cable.
You will have to activate RADIO or TV on your Beo4 to turn on BeoLab 3500 and get the sound of your Ipod (or any other audio system, of course).
That's what I'm doing with my BeoLab 2000 in the living room, I was missing a Masterlink cable of the right length to connect to my BeoPort box which is in the same room, so connected the 2 like this and it works! Selecting another source on Beo4 will mute the 3500, since the default sources are always TV or RADIO (pressing "play" on the 3500 won't bring you any sound either).
Enjoy!
Reunion Island is greeting you!