I'm not entirely certain about this, but many real 1911 parts will fit on KJW/WA 1911s. There is a good in depth discussion about this on airsoftplayers.com.
If I recall, the mainspring housing is one of the things that can be changed out with some modification, so you could buy a real one and make it work.
Alternatively, you could drill a hole (a la Glock) and run a lanyard through it.