Godhood was how I accomplished the immortality of one of my NPCs, via a specific deific role giving them Divine Rank 0. Not a god, but has plenty of perks such as high Spell Resistance, maximized HP, and...immortality. On how not to get these Divine Ranks without DM fashioned scenarios, there's always the option of becoming a Proxy.
While it would involve plenty of trickery (the Elan are likely protective of how it is they transform others into another being), there's always the option of storing all of your memories/experiences into some item in order to be found later. I'm certain any powerful psionic (the ruleset Elan is made for) could accomplish this. Immortality through one's continually stored memories...hmmm...