Rigging A Crossbow

I’m currently working on this crossbow which I hope to submit to the Team Fortress 2 contribution site. This is what I have so far…

http://i50.tinypic.com/2ivhu0.jpg

I have an armature rigged up for the bow and string, but I wanted to know how I could link the last bones in the string to the last bones in the bow (hopefully this and IK will realistically bend the bow back when the center of the string is “pulled”). Any help would be great, thanks.