Honestly.... I liked Morrigan since the start, she was very cool and mysterious and.... I also have to admit she is somewhat beautiful because of her exotic features.... and because of my fascination I included her in my party, ALWAYS, I never thought of removing her because she was so damn helpful & interesting =) but.... when I learned about the ritual.... letting my character's Alistair sleep with her NEVER crossed my mind.... I mean, who would want you yourself sit in another room while your man was being laid in another room with a totally hot chick? No doubt, he would somewhat like it... or try to like it... since alistair is still a man, no matter how faithful he looks... I HATED Morrigan since then... but I still begged her to stay because i needed her in the final battle, but you can't get everything so she still left....So during my first playthrough my initial plan was to sacrifice myself... But when I finally killed the archdemon... He stops me and does it himself,,,, no matter what I say to him... and that led me to thinking if it was better to let Morrigan bed him... since it was only a one time thing and I felt extreme guilt... but I still couldn't bear the nightmares it will bring if it happened....
Now I'm repalying with Equal Love Mod, if you still don't have it (which I highly doubt) I could give you the link =) though the AlistairxMorrigan sex scene from youtube still give me nightmares =(
To me, the most logical type of mod would be for one or more companions to undergo the joining with Riordan and have one them make the sacrifice. It always puzzled me a little when I learned that Riordan could actually perform the joining with Loghain that nobody stopped to consider the possibility that my talented and faithful companions who have followed me through hell and back wouldn't volunteer to or accept becoming a Grey Warden. Particularly after you learn that ONLY a Grey warden can slay the archdemon.
I'm rather surprised that Riordan himself doesn't suggest it considering the desperate need for alternatives in case the three existing Grey Wardens don't survive. The more Grey Wardens, the better and Grey Wardens are supposed to do ANYTHING to stop a blight...even if that means knowingly putting your friends lives at risk of instant death. I could see Oghren and Liliana being willing. Possibly Zevran if your influence is VERY high. Wynne is already living on borrowed time and would probably be quite comfortable with the idea. Stne might even be a possiblity, though this woud conflict with his duty to his people. For those with the Ser Gilmore mod, he is an obvious choice.
A more amusing alternative might be Dog. After all, hasn't he already survied the Darkspawn Taint?