Can I simulate a hook using Devel's PHP execution?
The main problem with simulating any hook is that the hook only makes sense in the context of whatever is doing the invoking.

Hooks get fired either from a module_invoke() or a module_invoke_all().  These functions assume that the hooks have already been found and exist in the registry.  They also take into account the invocation order (by weight, then alphabetically by module name).

The process and preprocess hooks are little different as the hook parameters get passed in by reference, and there is a more complex calling scheme, so the order really does matter for what is present in $variables.

The net result is that you can't really fake out a hook without actually implementing the hook somewhere.

Personally, I keep a devel module around with the most common hooks stubbed out as empty functions.  I also stub out common process/preproess and form alters.  This way I can dpm() something whenever I want without needing to do a cache clear.  For example, I have a high-weigh module with 

/**
  * Implements hook_form_alter().
  */

function mytestmodule_form_alter(&amp;$form, &amp;$form_state, $form_id) {
  // dpm($form_id, 'form_id');
  // dpm($form, 'form');
  // dpm($form_state, 'form_state');
}


in it.  This way, Drupal already knows about the hook in the registry.  All I need to do is uncomment / edit the function as needed.