Best Ways to Remotely Wipe or Encrypt Windows Server 2008 R2?

You could go with VeraCrypt since it's open source and works on Server 2008 R2. It allows you to encrypt the entire disk remotely, just make sure to use a strong password and multiple encryption ciphers. Once encrypted, rebooting will make any recoverable data virtually inaccessible.

Consider writing a scheduled task that overwrites critical data and user accounts. Using commands like 'sdelete' and 'cipher' could accomplish this. Deleting essential boot files would make the server unbootable, fulfilling your requirement to prevent reuse.

According to my knowledge, you technically don’t need a TPM for BitLocker on Server 2008; it should still prompt for a startup key. However, it might be useful to use scripts that overwrite data. You can use 'cipher' to clear free disk space or 'sdelete' for more thorough wiping.

It's not paranoid to plan for data security, especially if the customer insists on secure disposal. Depending on your access, you could utilize a virtual CD/USB image and run a data wipe program remotely. But if you can't access them physically, using diskpart to clean the partition would effectively brick the server.

Have you thought about simply using BitLocker? Even though you're lacking a TPM, you can set it up without one by choosing to print the recovery key, which is handy if you set the printer to a non-existent one! This way, you can still secure your servers with a password.