That should work.
If it was me, and I would do what mountain suggested.
Solder short pieces of wire to each pin, then connect them all together.
This would be a lot simpler than using jumpers between the pins.
In the attached drawing, I show how I would do it, if you are only running the power supply through this plug and nothing more.
There are nine pins, Im using 4 for positive, and 5 for negative.
This will work and should carry pretty heavy loads, but lets examine this for a minute.
The current will flow through each pin. If the resistance is exactly the same on each pin, then the current will be exactly divided between the pins.
Example: if the total current draw is 4 amps, then each pin in the 4 pin group will carry 1 amp.
But if a pin develops a bad solder joint, or breaks off, then that pins load will be placed on the other pins, making each pin carry 1.34 amps. If another pin breaks, the current on the remaining two will be 2 amps each.
So what you are doing is perfectly ok, but just keep this in mind.