It’s pretty simple, and I’ve actually had this conversation when we were receiving meals while someone was very ill at home.
Considerate baalabusta: Do you eat xyz’s shechita?
Me: yes.
CB: wonderful. Do you eat such and such hashgocha?
Me: No.
CB: what about abc hashgocha
Me: Yes.
CB: Ok, I’ll be by around 2, k?
Me: That would be great, thank you very much.
If both people are basically polite and curteous and the giver does keep kosher, you can avoid any kashrus problems just like that in under five minutes. I’ll admit, if the giver does not keep kosher, a lot more tact is required.