Make your gradient into a symbol and then map this onto the surfaces of your 3D object. Search "Extrude & Bevel" in the help files and look at the sections on mapping artwork to a 3D object.
steve
I hate to break it to you, but a bevel is 3-d by default. How can you have a bevel on a 2-d object? Beveling requires a certain depth, which requires a certain thickness of the object, which in turn requires it to be 3-d, or at least look like it's 3-d.
I also think, but this is only my opinion, even if it's an opinion I share with a great many other designers, that bevels are sooooooo 90's...
Hi Steve!
Bert
Select my gradient filled object
Copy / Paste in Front
Fill the duplicated object with white
Use the 3D Bevel effect, set the viewpoint to Front, and apply the desired shading to the white object. To avoid graying out your front surface, you will probably want to add an extra light from the front center (see More Options), while the other light remains off-center so that the bevel shading is darker at the bottom than the top.
Change the Transparency blend mode of the beveled object to Multiply
But Bert is right, bevels are so 90's. I wish I had time to update my genealogy web site (designed in 1996, with loads of beveled graphics and horizontal rules) to not look so outmoded.