The soulknife is among the crappiest base classes in the game.
Despite this, I'm wondering if a few very simple things couldn't easily bring it up to Tier 4. Basically, I'm just giving it ACFs without penalties here, and honestly this was very spur of the moment and not super developed.
Grant it the bonus feats (as the soulknife bonus feat ACF from Mind's Eye) at 3rd, 7th, 11th, 15th, and 19th level, but do not remove the sudden strike ability.
Grant it hidden talent instead of wild talent (ACF from Mind's Eye)
Grant it a shadow bow and improved shadow bow class features, as the shadow soulknife Racial Substitution levels from Dragon Magazine #330. If you don't have access to that, you definitely shouldn't look it up on 4shared. That would be very unethical.
That's about it. Getting 5 bonus feats and a bow probably isn't enough though, so here's some further expansion that doesn't just give it ACFs without trading anything in return.
Give him an adapted version of soulbound weapon (the Psychic Warrior ACF from Mind's Eye) that effects his mind blade whenever he summons it. This brings the total bonus he gets on his mind blade up to +9. You might have to switch the levels around though.
Possibly manifesting powers as a Lurk (from Complete Psionic) or as a Psychic Rogue.
Maybe...spamming astral constructs as the Divine Mind ACF (from Mind's Eye...you've got enough links by now ) and flavor it as a sort of creature made out of your mind blade?
If you give him powers as a Lurk, mantles might also be good to have.
Feedback on this is appreciated, although I wrote it up in less then twenty minutes