SMS URL scheme on mobile fails validation

Developing a mobile site here. I tried to use the 'sms:' URL scheme in a menu item to invite contacts to the site. Relevant code:

'href' => "sms:?body=" . elgg_echo("app:invitation:body"),

However this gets normalized in elgg_normalize_url() in engine/lib/output.php: 265. As a workaround, I added 'sms:' along with 'mailto:' in the same file in core and it works.

Is there a way to achieve this without modifying core. I didn't have to modify anything so far and I'd like to keep it that way to keep the maintenance simple.