Take a look at

org.eclipse.swt.awt.SWT_AWT.new_Shell(Display, Canvas)

I've never tried it, but in theory that should allow you to use it. My  
experience with the SWT_AWT class (from eclipse 3.1) was that it was a bit  
flakey (spurious exceptions, some screen refreshes don't paint right, and  
the window manager occassionally shows windows open for each component).  
It's good for temporarily integrating modules from the two toolkits, but  
you will probably do yourself a big service in porting your code into one  
toolkit.

HTH,

-Zig