Yeah, it's doable...refinements needed, but general idea works.
Z = peaks(20);
[~,hCF]=contourf(Z,10);
hAx=gca; % save axes handle main axes
hCB=colorbar; % add colorbar, save its handle
hNuCBAx=axes('Position',hCB.Position,'color','none'); % add mew axes at same posn
hNuCBAx.XAxis.Visible='off'; % hide the x axis of new
posn=hAx.Position; % get main axes location
posn(3)=0.8*posn(3); % cut down width
hAx.Position=posn; % resize mmain axes to make room for labels colorbar
hCB.Position=hNuCBAx.Position; % put the colorbar back to overlay second axeix
hNuCBAx.YLim=[-22 22]; % alternate scale limits new axis
ylabel(hCB, 'A','Rotation',0,'FontWeight','bold','VerticalAlignment','middle')
ylabel(hNuCBAx,'B','Rotation',0,'FontWeight','bold','VerticalAlignment','middle')
hCB.Position=hNuCBAx.Position; % put the colorbar back to overlay second axeix
results in
I overshot the width reduction a little and it's kinda' kludgy to have to move the original colorbar back to its original position when change the other axis size but there's an internal callback function that ties them together...
