[Duugu]

You could hook the OnClick event of the frames.

for container = 1, 5 do
    for item = 1, 36 do
        _G["ContainerFrame"..container.."Item"..item]:HookScript("OnClick", function(self, button) 
            if IsShiftKeyDown() and button == "MiddleButton" then 
                print(GetItemInfo(GetContainerItemID(self:GetParent():GetID(), self:GetID()))) 
            end 
        end)
    end
end

Another way doing it would be to hook Blizzards ContainerFrameItemButton_OnModifiedClick(self, button).

Like

hooksecurefunc("ContainerFrameItemButton_OnModifiedClick", function(self, button) 
            if IsShiftKeyDown() and button == "MiddleButton" and self:GetParent():GetID() <= 5 then 
                print(GetItemInfo(GetContainerItemID(self:GetParent():GetID(), self:GetID()))) 
            end 
        end)

I bet Phanx likes this one more because it's using only one hook and not 5x36. ;D