Ho-Oh, Red Gyarados, and Sudowoodo are not roamers so I don't know why you have to continually beat the pokemon league to RNG them. If you killed them, then just respawn them one time and RNG them separately. Note that Red Gyarados is not Method K though and very few people actually have successfully done one. It seems that Nexus and Expert Evan knows how to do the Lake of Rage monster.
For Raikou, Entei, and one of the Lati twins, you just want to kill one off (the one you want to RNG) and let the other two roam ideally so that you can verify what delay you're hitting. Riski went through quite some trouble for hers so I imagine she'll have a much better memory than I in this category.
Since I don't believe you can call Elm in Lance's room, the best bet it would seem is to kill off only one and leave two roamers out. This way, you can verify for your delay and don't have to repeat the process again. An AR helps here of course.