Use multiple URL arguments to prepopulate multiple entity reference fields
You can follow the same approach given in the example.

You will need to rewrite the link from 

http://example.com/contactform?field_name=12345


to  

http://example.com/contactform?field_name=12345&amp;field_name_second=4567&amp;field_name_third=890


This should do the trick for you.

If you want it to look more elegant, then you can just pass the entity id of the referring object and then write some code to pre-populate the values based on the given entity.