Upgrading Ax reports with customization from R2 to R3

Hi Everyone

A customer has several existing Ax SSRS Reports - like SalesInvoice - which has several customizations on it.

These customizations are in an Ax 2012 R2 environment. They now want to take the customizations over to an R3 environment. Also, the customizations lie on a different layer in R2 to what they need to be in R3.

Is this possible and what is the best way to do this?

An xpo export doesn't' seem like a good idea; A model export doesn't seem possible because of the different layers; 

So far, the best option seems to be rework. (ie. Recreating the customizations on the new environment), but that sounds impractical.

What is the best way to do this?

Thank you