Custom pragmas in Clang


I am trying to enable some source-to-source transformations which are enabled using pragmas. I mostly just want insert calls to a library whenever I encounter a pragma. For example something like this

#pragma callout
x = foo();

would become:

x = foo();

Is it possible to implement something like this as a Clang plugin or using the libtooling interface? I know how to hijack documentation comments to make this possible, but I would prefer to use a pragma. I would rather avoid modifying clang itself to enable this.