It depends on how you define before but below is one technique.
When you create a publish profile with VS2012 it will create you a .pubxml file in the Properties\PublishProfiles folder (My Project\PublishProfiles for VB). These are MSBuild files and you can edit them to customize the publish process. In your case you can inject a target into the publish process, before the publish actually occurs. You can do that by extending the PipelineDependsOn property as below.
<PropertyGroup>
<PipelineDependsOn>
CustomBeforePublish;
$(PipelineDependsOn);
</PipelineDependsOn>
</PropertyGroup>
<Target Name="CustomBeforePublish">
<Message Text="********************************** CustomBeforePublish ***********************************" Importance="high"/>
</Target>
FYI regarding the customization of .wpp.targets, that was the only technique which we had for VS2010. My recommendation here is as follows; customize the .pubxml file for most cases and to only create a .wpp.targets file if you want to customize every publish of the given project.