That is indeed possible. Right-click on the toolbar, select "More commands", go to the "Commands" tab page, select the "File" category, scroll down to the "Open" (Open a workset) command, and drag & drop it to the toolbar.
When I open workset it always sets the focus on the last window (if I have more widows open). Is it possible for a workset to remember the window (or even better - the exact position in window)?
I see that this is not implemented in beta 3. Do you think you could do it for final release?
Since I do two things at the same time (bad habit I know...) I switch worksets a lot and keeping the focus on window would help.