Ooh I didn't even know that was a thing in normal wikitext... :D I'll have a look, I would have expected that to work as I thought MWC used the same parser as normal wikitext.

hmm, looks like there is some sort of pre-parsing for this trick: https://en.wikipedia.org/wiki/Help:Pipe_trick

Okay, this is T4700

You'll probably want Parser's preSaveTransform.

Quick example code you can run in /maintenance/eval.php to try it out:

global $wgParser;
$user = User::newFromName( 'Jack Phoenix' );
$title = Title::newFromText( uniqid( 'tmp' ) );
$options = ParserOptions::newFromUser( $user );
echo $wgParser->preSaveTransform( '[[Special:RecentChanges|]]', $title, $user, $options );

This outputs [[Special:RecentChanges|RecentChanges]].

oops hold on

Change 328927 had a related patch set uploaded (by UltrasonicNXT):
Use preSaveTransform to allow the pipe trick among others

https://gerrit.wikimedia.org/r/328927

Change 328927 merged by jenkins-bot:
Use preSaveTransform to allow the pipe trick among others

https://gerrit.wikimedia.org/r/328927