I’m sorry to tell you that the publish.xml file which VS2010 uses was not designed to be used in this way. In fact it was not even designed to be checked-in/shared with others.
The logic for reading/writing those files are strictly contained inside Visual Studio and not available through MSBuild. So there is no straight forward way of doing this today. You have to pass in the individual property names/values when you call msbuild.exe. You can see a similar question that I answered at Team Build: Publish locally using MSDeploy for more info.
Note for VS 11 Developer Preview
Just so you know we have addressed this in the up coming version of Visual Studio. You can see if by downloading the VS 11 developer preview. Now all the profiles are saved into their own files (under the PublishProfiles in the Properties node in Solution Explorer). They are now designed to be checked in and shared with team members. These files are now MSBuild files and you can customize them if you wish. In order to publish from the command line just pass DeployOnBuild=true and set PublishProfile to the name of the profile. For example:
msbuild.exe MyProject.csproj /p:DeployOnBuild=true;PublishProfile=MyProfile