ShadowDrawer broken - anyone have a fix?

We've been relying on the ShadowDrawer shader to cast shadows from CG elements onto live action in AR through Vuforia. It's been working perfectly.

Apparently, a there's a call to a routine in the shader that's been deprecated for a while but has now been removed from 2018.

this is the broken line:

half atten = LIGHT_ATTENUATION(IN);

Supposedly LIGHT_ATTENUATION has been replaced with UNITY_LIGHT_ATENUATION but it's not a direct swap.

We need 2018 to patch a vuforia/iOS 11.3 bug.

Has anyone been able to patch this or possibly suggest a replacement? Effectively I'm basically asking for a straight forward "shadow matte" shader.

Thanks in advance!