Take as look at this... You may be able to adapt a clamp in a similar manner, not trying to sell you this system.
Just an idea. I've seen guys take a spare coupler and a hammer before too. Just have to make it pop a little pressure, doesn't have to completely install.
You could make a tool with a ball valve attached to a coupler. Close the valve, and pop the coupler on with a hammer. Then remove it, and open the valve to drain the collected fluid to use the tool next time.
Just be careful with fluid under pressure. I wouldn't ever try to attach with the hydraulic pump ruining, of course. And never try to find a hydraulic leak with your hand... The high pressure oil spraying out will cut into your skin like a water jet cutter, and causes sometimes fatal injury.