Setting address information in packet info structure for conversations

I have a dissector for a link-layer protocol for which I can dissect packets already. I need to implement conversations for my dissector for per-packet data, and would like to use find_or_create_conversation. I have already added my new address and port types to epan/address.h, epan/address_to_str.c and column-utils.c.

How do I set the source and destination information in the pinfo structure so that the correct conversation data is found?

Sometimes my protocol is simulated over UDP for testing, and I'd like to use the same dissection logic regardless if it's over the real hardware or UDP. How do I ensure that any other source/destination data is clobbered so that only my protocol's data is present?