If the ABS brake system is not functioning the brakes function as non ABS brakes. So, what do you mean by "bypass" the ABS system.
You can eliminate the ABS by gettiing a non ABS master cylinder, say from an 89 SHO or a non ABS SLO or Sable, and the non ABS proportioning valve, and the matching brake lines.
Look at a non ABS 89, or the appropriate service manual, and determine what if anything else you might need to convert to a non ABS SHO.
You could just pull the fuse for the ABS, or disconnect the pump and/or Control Unit. Then the ABS would not function, and the brakes would work as non ABS brakes, assuming there is no hydrolic malfunction in the ABS.
Why would you want to do that? ABS has been in use on aircraft for over 50 years, and is a proven system. It gives you better control and shorter braking distances in hard stops or slippery conditions. rangerj