Cavian

I had to log on to a second account to check because I already have the Omega Prestige on my main one but here's what I did: Go to Spider-Man in the roster, choose any costume and select to play as this hero. Go back into the roster, with Spider-Man selected press triangle (unlock), it'll bring you to the page to pay for Spider-Man with either Gs or Splinters. On the Unlock page move left and it'll offer you his Omega Pack, select that. Pay for the pack using 1 Splinter. Done.

If you go to Storm, Psylocke, Magick, Jean Grey, & Spider-Man in the Roster there will be offers to buy their "Omega Pack" for 1 Splinter. I highly recommend doing this even if you're not going to use the character. After you "buy" the pack, switch to the character and go back into the roster, select the option to activate their Omega Prestige. This will instantly give you their double synergy bonus to equip on any character but the secret kicker to this is that the character counts as having reached level 60 for the bonus XP percentage. You'd still need to level them up again because the level 60 trophies require your 5 characters all be level 60 at once but in exchange you get a free legendary, bonus XP, and a very powerful character (or 5).

June '11 with 171, and despite picking up a bunch of games on Black Friday it looks like December is lagging right now.