We don't have any guides or documentation, but they should be able to see how we do it. If they want to contact us directly they can and we can add them to our development repo for them to add their files. However, with how hikashop works and the vast configuration options I'm not 100% sure how sustainable it would be to have native support.
Thank you! Now moved, Hikashop is a whole different ball them as to how to handle there code. They have a lot of php within view files which makes it more complicated to create overrides for and support for their updates etc.