In *theory* the same way in theory I can go out to the local 7-11 buy 3 lottery tickets and hit the jackpot on all of them.

ANYONE can get insanely lucky and find a block with not a lot of hashpower. IF you have ignored the previous block you can then broadcast your own in it's place. BUT all the other nodes have already SEEN the block you ignored so they will not accept yours. You then have to get insanely lucky a 2nd time to find a 2nd block that you would build on top of the other one you found and broadcast that. And do all of that BEFORE some other mining pool found a block on top of the proper chain.

You might be able to do it with less then the accepted amount of hashpower needed. You would be better off buying lottery tickets.

-Dave