One viable option could be to partition your drive. Setup the minimum amount you need for booting, then use PGP Whole Disk Encrypt to encrypt the other partition. But, in all honesty, that is what Filevault would accomplish.
Hmmmmm.... there are no solutions BTW for the Mac... aside from replacing your internal drive with an encrypted drive, but 256bit is a little silly. RocSafe only supports up to 192 if necessary.
What I can tell you, is what the Home Office wants to accomplish is this. They want to ensure that if a laptop is stolen, that the information, no matter what state the computer was found in, that nothing can be extracted from it.
FileVault will accomplish this goal, assuming you store your data files in your home directory pertaining to the business.
Honestly, I would push back. Say, you know, I have a Mac with all these wonderful encryption built into the operating system. It would accomplish the same thing. I will erase my free space religiously. Life will be grand. I bet they will think "OMG - He has a Mac?" and will either be hard nosed about it or go, "Okay".