Okay, so the answer to your previous question is that you don't prove that you have lived there for 2.5 years, because that would be proving to them that you were there illegally and would probably ensure that you are not let into the UK ever again.
This puts you in a bad spot as far as trying to get any other kind of visa, because you run the risk of being asked about previous visits to the UK. I haven't been through any visa procedures yet, so I don't know if that's a common question.
Options include HSMP (Highly Skilled Migrant Programme), getting a work permit, or fiance or spouse visa (if your partner is opposite sex). There is an unmarried partner visa, but you have to show that you have lived together in a relationship akin to marriage for 2 years, and it seems you won't be able to do that.
That's all I can think of. Maybe other folks know of other options.