Step One - go do the efreeti quest given by Ronar Flametip in PoTranq. It gets you into the zone.
Step Two - talk to Neerin. He'll not speak with those legitimately flagged for Sol Ro's tower, only those who did the alternate access quest.
Step Three - collect the 3 key parts:
1. "a sun lord" (73, single-groupable) at the entrance of the Protector of Dresolik branch.
2. "an efreeti baron" (72, single-groupable) at the start of the Jiva branch (first efreeti you'll find, with some mephit guards).
3. in the entrance of the Xuzl branch there's a nameless skeleton on the floor. /open it like a container and loot the 3rd part.
Step Four - turn them in to Neerin. Receive no actual key or noticable character flag.
Step Five - scratch head. Reportedly doesn't actually give you access to the chamber? Maybe getting flag-dragged inside and killing Sol Ro will complete proper tower backflagging? Who knows. (Please post if you do. :) )