Set the first/last x values to min(x)-2/max(x)+2, respectively, then set the ticklabels for those two manually.
y = [2 2 3; 2 5 6; 2 8 9; 2 11 12]; % from bar() example for grouped
x=[0:length(y)-1]-2; % simulate similar x
y=[y(1,:);y;y(end,:)]; y(1,end)=0; y(end,1)=0; % augment y similar to desired
x=[x(1)-2 x x(end)+2]; % fixup the x vector with gap
subplot(2,1,1)
bar(x,y); % default look to match
subplot(2,1,2) % now fixup the ticklabels as desired
bar(x,y); % base plot
LABELS={'WP','SHVK'}; % the specific group labels wanted
hAx=gca; % get the axis handle
hAx.XTickLabels([1,end])=LABELS; % write those two in place of default
