Alternatives to WCM? Dairy challenge fail?

DS is 15 months old, and we did a dairy challenge at 11 months which he failed.  His pedi GI wants us to do another challenge, and I'm a bit gun-shy to try.  We have an appt with a pedi allergist in November so we can see if it's a true allergy but my gut tells me it's not.  He doesn't start having a reaction until a few days into the dairy challenge and it's more of a behavior change (along with blood in the stool).  He doesn't get a rash, diarrhea, vomiting, etc. within 24 hours...so he COULD have an allergy but we'll see.  Anyway in the meantime he's still on 3 bottles (shame, I know--we've been trying to switch to the sippy and have tried 6 different kids, all of which he drinks water out of just fine but anything else he just tosses the cup) which we usually mix a bit of formula with rice milk.  His pedi GI says she'd prefer him to be on almond milk which I'd prefer too, but the two days a week he's at daycare he wouldn't be able to have that because he's in a nut-free room.  I guess all this babbling is just because I don't know what to do.  I don't know if I'm comfortable doing another dairy challenge again (how soon did you try again after the first "fail"?).  I don't know how to get him off the bottle onto just a sippy when I don't even know what I'm transitioning him TO.  I also am curious, if your LO drinks almond milk, what kind/flavor/calorie amount you use.

Sorry for the rambling...just looking for some kind of direction.  Thanks!