This forum is about the Future, not the Past - we can obviously not put new features in past engines like A7, A6 etc. But when you need more flexibility for ignoring entities in old versions, here's a suggestion.

Use the group parameter for collision groups, just as in A8. Write your own Ignore function that runs an ent_next loop and sets the FLAG1 of all entities that match the desired groups. Then call the collision function with IGNORE_FLAG1, and afterwards run the loop again and reset FLAG1.

This should not make the collision much slower, and gives you about the same behavior as the c_ignore function that didn't work for A7.