Ok - I think I have this working.  I was able to compile our application under a VMware guest that didn't have any of our developer tools (RAD Studio, EurekaLog, etc.) installed.  Basically I have a Compiler folder with these files:
Turns out you only need a few files.  Basically these files:
02/05/2008  05:13 PM            89,088 BorDebug.dll  
11/02/2009  06:02 PM            57,344 Borland.Build.Tasks.Common.dll  
11/02/2009  06:02 PM           147,456 Borland.Build.Tasks.Delphi.dll  
11/02/2009  06:02 PM            49,152 Borland.Build.Tasks.Shared.dll  
11/02/2009  06:02 PM            20,480 Borland.Globalization.dll  
08/19/2009  05:00 PM            22,370 CodeGear.Common.Targets  
08/19/2009  05:00 PM            32,928 CodeGear.Delphi.Targets  
11/02/2009  06:02 PM         1,328,128 DCC32.EXE  
02/25/2010  08:17 AM           979,456 ecc32.exe  
11/02/2009  06:02 PM           314,368 lnkdfm140.dll  
02/25/2010  08:11 AM            40,960 Process.exe  
08/19/2009  05:00 PM            75,264 rlink32.dll  
06/15/2010  08:41 AM               185 rsvars.bat  
Maybe I could snip a few more of these files out as well.  We also have a components folder that has all of the built-in VCL files (basically the lib and Indy10 folders) and our third-party components.  In Delphi I made the Library path setting blank — this step is key.  I then put that Library path setting in the specific project options.  We used environment variables to specify where the built-in and third-party files were.  These environment variables are set in RAD Studio, and then can be set via command line when performing the release compilation.  So we have a BAT file like this:
SET BDS=C:\_Releases\Compiler
SET COREFILES=C:\_Components\D2010
SET COMPONENTS=C:\_Components
SET LANGDIR=EN
Our library path looks something like this:
$(COREFILES)\lib;$(COREFILES)\Indy10;$(COMPONENTS)\EurekaLog;$(COMPONENTS)\Jcl\source\common;$(COMPONENTS)\Jcl\source\windows
Now in our virgin VMware session that just has MSBuild and the raw files described above I can call these commands:
msbuild project.dproj -t:rebuild /p:config=Release  
ecc32 --el_alter_exe"project.dproj"
Which builds our application. Granted we are just using the Delphi32 personality which simplifies things, but for us I think this will work fantastic.