I have a template for building out all skus of the same solution in parallel.
This is the same concept as Stijn's approach that uses an ItemGroup as a project definition rather than a series of options for a particular property + the msbuild task will build both at the same time, saving you time and bubbling up any configuration issues when building in parallel.
<Project DefaultTargets="Build" ToolsVersion="4.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
<ItemGroup>
<SolutionToBuild Include="$(MSBuildThisFileDirectory)\MyProject.sln">
<Properties>DeployOnBuild=True;PublishProfile="Dev Server"</Properties>
</SolutionToBuild>
<SolutionToBuild Include="$(MSBuildThisFileDirectory)\MyProject.sln">
<Properties>DeployOnBuild=True;PublishProfile="Prod Server"</Properties>
</SolutionToBuild>
</ItemGroup>
<Target Name="Build">
<MsBuild BuildInParallel="true" ContinueOnError="true" Projects="@(SolutionToBuild)" />
</Target>
<Target Name="Clean">
<MsBuild BuildInParallel="true" ContinueOnError="true" Projects="@(SolutionToBuild)" Targets="Clean" />
</Target>
</Project>