Well this is a popular topic all over the forums in different shapes and forms (O: Maybe it needs to be gathered in one place somehow as there are some neat looking methods and approaches out there. Anyway...
Yes Willr I did try applying to SiteTree with this outcome
1. Using add_extension(SiteTree,'HidePages') in the HidePages _config.php certainly did not spawn extra ParentIDs or crash anything BUT it did not use the alternate stagedChildren() function (verified by echoing an HTML comment and viewing page source).
2. Hacking (yay) the SiteTree.php to add 'HidePages' to the list in $extensions does work but is not desired as it is a core hack and not a polite overlay.
Unless there is another way to override this function I will continue on with investigating the rumors of an augmentedStageChildren function that may be worth a look.
However if you want to use the existing v0.27 module then this will work with 2.4.2 (and modified to have 'Peers' tab for child's list of parent's other children) following the instructions in INSTALLING.
Thanks to Willr for his time - I'm sure he has plenty of better things to do.
[[ V0.30 IN LATER POST. I'M LEAVING 0.27 HERE IN CASE SOMEONE WANTS THE BROKEN VERSION FOR ALTERNATE APPROACH OR MAKING IT WORK ]]