Using Vin pin on Arduino with a shield
When you are realy in such a hurry, you could attach the wires of the battery with some tape to the spots I marked in the picture. Maybe the bottom is easier to get the wires stick to.



When I remember right (1) is +9V and (2) is GND. The integrated diode should prevent damage, if you connect it the wrong way.



After taking a look at the schematic I would mean, that connecting the battery to VIN is save. Just be carefully not to change polarity, because you skip the protection diode. This forum thread approves my thought.

In the comments you asked, whether you could use an additional external diode to increase safety. In my opionion this is not neccessary. It is just getting more complex.
Get two colored wires (black, red) and connect them to the battery, so you can immediately see whats GND. When you connect the wires, just pay attention.