Relay Help

[badjesus]

Hey guys, I have some halloween stuff I am trying to do.
I went down to Princess Auto and got a few pneumatic rams and found some cool pneumatic 12v solenoids. 

I then went and picked up a Card Access Motion Sensor and am using a spare HC300 with the one relay output right now. 

 

What I am going to do is hide a skeleton in my garbage can. When someone walks by, the lid will pop open real fast and I will have my sonos player play a screaming noise. It should scare some people pretty good

Everything is working just fine at first. The problem is, with my relay set up, NO is constantly sending 12v to the one part of the solenoid keeping the unit in the down position.
When the relay toggles in C4, it removed power from this and switches it to the NC on the other side and the ram pops up. Because it is sending constant 12v to keep the ram down, it is getting REAL hot. 

Ideally, I should just use two relays, but I don't have that ability with just this one spare hc300. Because this is going outside, I don't have much other choices. 

Can anyone think of a way to only pulse to NO? I don't think this is possible at all, is it?
 

 

 

Also, is anyone aware of a relay board that there is an existing C4 driver for with dozens of relays? I wish I could find a device that just has 24 relays with one RS232 port.