When I spoke with Origin on the phone a few months ago they told me this is completely impossible.
I had an origin account previous to getting my PS3 that had one email address but my PSN account had a different email address. Apparently when you log into an EA game from the PS3 it automatically looks for the email address that you have as your sign-in name for PSN to link the origin account. If no account exists with that exact email address a new one is created for you.
When I spoke to origin about this they said the only option was to change my PSN sign-in email address to the same one I have for my origin account. They told me that if I did this the next time I went online with an EA game on my PS3 it would automatically link my Origin and PSN accounts and the other account that was created would then automatically be de-linked. The also said the setback to this would be that any game progress would be erased.
So I changed my PSN login to match the email address that I had associated with my original Origin account and logged into a brand new EA game (battlefield 4) that I had never played online before. Even though my PSN email address had been changed my account remains linked to the new Origin account they created for me.
Since that was the only solution Origin could provide at that time I am inclined to believe that there is simply no way for me to link my PSN account to my Origin account. I wll forever have a second Origin account that links to PSN and has no games bought on it while still having my original Origin account with all of my PC games on it.
Super annoying but there is nothing you can do until EA decides to let us un-link PSN and Origin accounts.
