Unless I'm reading it wrong, the final rite (Transforming the Spirit) requires a lab total equal to the sum of all your Arts. The lab total is calculated off of the highest Form + Technique; therefore the equation basically becomes:
(Int + MT + misc bonuses) vs (All Arts except highest pair)
Which, even if you're raised the others only to 5 in order to teach an apprentice, gives you 13 x 5 = 65. Which doesn't seem achievable.
Ordeals (as mentioned)
Assistants (including familiars/apprentices - could be huge with a decent Leadership score)
Magical Focus / Potent Magic (could be huge if a focus applies)
Lab bonuses (set it to the right Technique and Form)
Lab routines (these might conflict some with assistants)
Hard? Not really. You only need a high Warping score for that one season. Let's assume you have a score of 3 in Faerie Magic with a specialty in Becoming, giving you an effective score of 4, not that it really matters much. That shouldn't be so hard to acquire. Safeguard yourself in your lab. Spend the first day of the season giving yourself 1 warping point at a time using a level 5 spell. Given a reasonable Aura and a decent score in either Creo or Vim and a touch of the other, you can cast this spontaneously safely (without fatigue) ten times a minute, and you don't have to invent it. Let's say you reach a Warping Score of 20 (less than 2 hours of actual casting). 20x4=80. If that's not enough, spend a little more time casting that spell.
Also note that Ordeals lower the level of the ritual instead of raising your lab total. This also helps bring you within the cap.
I hate that Warping above 10 is allowed. It makes longevity have no upper limits. But yes, it's a valid RAW option.
I generally find a Lab Total is about half Arts and half miscelleneous bonuses (familiar, aura, Int...), but covering ALL of your Arts can still be rather difficult... I think the Ordeals are the path that is supposed to be taken.