stealth for ps2 is non-existent - the chip is either on at boot or off at boot - no way around it for the following reasons:
DNAS operates by checking the ps2's bios. The modchip, when enabled, replaces chunks of the bios which essentially makes stealth impossible. That's the first method used for the DNAS check - see if the console is modded. The second step of DNAS is to check the media if it is an original. If it isn't, then you won't be allowed in. The chip can't falsely give info because the bios data is verified through the DNAS server.
If there IS a way around DNAS, it's EXTREMELY illegal and whoever gets caught using it will be in craploads of trouble. You would be violating SEVERAL laws trying to bypass. 1) A violation of the DMCA, 2) it's essentially going to require hacking of someone's servers.
If you wanna do that, you're talking to the wrong people...
if you want to go online, then STOP BEING CHEAP and BUY the game - keep the chip for your imports/backups