Custom Lighting - Attenuation without shadows

So I'm working on some surface shadersw ith custom lighting, and part of the effect is a fresnel rim that's supposed to appear when you put the object between the camera and the light source.

Doing this is pretty easy, it's just some dot products and some multiples, but the issue comes in with attenuation.

Obviously, I don't want this effect to suddenly disappear if a point light goes out of range, which means I need to apply the light attenuation. However, Unity's light attenuation system bakes the shadows into it, and since my effect is supposed to occur on the opposite side to the light, it's always in shadow (assuming the light is casting a shadow). This means that if I apply attenuation naiively, the effect vanishes.

Now, I understand the usual way around this is to modify the fragment shader and calculate attenuation without shadows, but I'm working with a surface shader, and so I don't have access to the call to the lighting function.

What I can do, of course, is access the code generated by the surface shader, and modify that. This works, but is a little messy.

I'm wondering if there's a neater way to access this from the surface shader, because it would certainly save a lot of time if there were.

If you're not aware of what I'm talking about, I'm referring to the atten value given as an argument here:

 inline half4 LightingCustom(CustomSurfaceOutput s, half3 lightDir, half3 viewDir, half atten)

Which is computed in the (automatically generated) fragment shader like so:

 UNITY_LIGHT_ATTENUATION(atten, IN, worldPos)

In theory, I could grab the information from that macro, but it appears to only be accessible from the fragment shader, and I only have a SurfaceOutput struct.

Any help with this?