I'm wondering if any of you guys know the global variables I need to input to get Hrothgar to bring my party to Ulcaster ruins. I asked him to leave the party before exiting Irenicus' dungeon because I didn't have room for all the NPCs present but since picking him up again he hasn't had anything to say about the second quest. Hope you can help.

Really, I don't understand how you play NeJ without Hrothgar. You would be killed immediatelly. But.... I beleive he is in Copper Coronet. Why you havn't room for Hrothgar? And what about Melora? And Leina?

I had Hrothgar in my party throughout the Icewind Dale section of the mod, but asked him to leave and wait for me in the CC while making my way through level 2 of Irenicus' dungeon because I needed to bring some other mod characters out with me. I went to pick him up again immediately afterwards but he hasn't mentioned Ulcaster in the days (game-time) since.

This is because you missed his starting speach, when you appear in Woakine Promenade. You should not kick him away. He is key character
And you broke part 2 I afraid. Use your previous save and never kick Hrothgar from party!