Against a typical foe that's two or more size categories bigger than the attacker's own, a typical attacker's attempt to grapple stops at Step 3: Hold because the attacker "automatically lose[s] an attempt to hold if the target is two or more size categories larger than" the attacker (Player's Handbook 156). The typical attacker's bonus on grapple checks can be literally infinite, yet even infinity is insufficient to allow the attacker to take hold of a foe two or more size categories bigger than it. The best halfling grappler that ever existed can't suplex the tarrasque—or even a lowly ogre—without your help.
So, without changing the attacker's or the defender's size category or form—and without Pun-pun style shenanigans—, is there a way for an attacker to hold a foe two or more size categories bigger than the attacker?
Allow me clarify that I'm not looking for that one race that can grapple too-big creatures but for generally applicable options available to any creature after it enters play as not that race. Workarounds are unacceptable—for example, no committing suicide on a boon trap of last breath until the DM rewrites the reincarnate chart to include goliath then gaining XP sufficient to advance a level then taking the goliath barbarian 1 substitution level.
The spirit of the question would have answers locate in a text a feat, spell, magic item, or similar material that doesn't change the creature's size or form yet allows the creature to get a hold on too-big foes. A class that permits this is a last resort and shouldn't have a race as a requirement for entry.
(Be nice to answers posted prior to 5 Sept. 2017 at 1 PM PST—those answers were posted prior to the previous two paragraphs.)
Note: The Races of Faerûn feat Jotunbrud (166) is no help here: it only increases the modifiers due to size and doesn't change the creature's size category. Similarly, the Dragon #303 martial arts style Stonegrind Wrestling (57–8) says that the creature is only "one size category larger for the purposes of grapple checks," rather than grappling generally. Further, the Dragon #300 prestige class flesheater (68–9) at level 2 gains the special ability flesh rip that makes it so the creature only no longer suffers size penalties on grapple checks. Even the game's finest mundane rasslin' class, the Champions of Ruin prestige class Black Blood cultist (44–8), doesn't normally overcome this size category limit. The fan-made grappling handbook "Hulkmania Is Runnin' Wild" focuses (albeit rightly) much of its attention on becoming bigger, bypassing—not altering—this limitation it. The closest I've found is the Dragon #342 halfling barbarian 1 substitution level special ability halfling rage that lets a halfling (only) while raging (only) count as Medium (only) "whenever doing so would be beneficial, such as while in a grapple" (90–1), which is pretty darn restrictive… and, given the wording, the DM may or may not allow the special ability to work for this purpose.
It was the special ability of the prestige class flesheater that reminded me once more of this limitation: it's a halfling-only prestige class that's good at grappling… yet that doesn't really seem to take into account that some of its best abilities are unusable on creatures with a size category bigger than Medium—like bigger creatures don't have flesh to eat or something. Does anything actually change—or even eliminate—this limitation on grappling for a halfling hungry for some tasty, tasty tarrasque?