I need help applying pricing according to customer profiles, rather than user details.

I have a custom field in the customer profile and I am trying to get the order to update the line item prices when the customer billing information/profile is selected.

So far I have tried various rules but I am struggling to get the custom field to become available for use.

I have tried the Entity as field option but haven't had much luck. However, I was trying this at the checkout completed event so I wonder if this is too late in the order stage. Ideally, I guess I would need to target the 'when a customer profile is selected for billing' event but it doesn't seem to exist.

The aim is to end up with a system where once the order billing information is called up, the line item prices update in accordance to a value held in the customer profile. (i.e. multiple by x to give a discount).

Has anyone managed to apply price variation by a custom customer profile field?

Or any ideas how to work this out by rules or php fired by rules?

Thanks,

Stefan