First, you need to find objtex_stg13.pak located in Steam\steamapps\common\Sonic Adventure 2\resource\gd_PC\PRS. Once you find it delete it. The game has a secondary file that didn't replace the SOAP ads[objtex_stg13.prs]. The game also uses .prs files but .pak files are dominant and are used first over a prs file.

The two effects of this guide are:
1) Sonic's face isn't plastered in the stage as much as it currently is(the Sonic Team ads are used instead of the SOAP ads in the pak file)
2) The SOAP ads are back

EDIT:This also works for Radical Highway(objtex_stg14.pak) and Downtown Race(objtex_stg52.pak)
EDIT 2: For anyone on the fence for this, there is absolutely no problem with deleting the .pak files for these stages. Deleting the .pak files simply tells the game to go use the older unedited .prs files.