Can I get my marriage extension stamped before the 30-day under consideration period ends?

As a rule, NO..

For extensions based on marriage you get the 30 day under consideration stamp, they schedule an in home visit during that time and then you go back on the date that stamp expires and get the rest of the 11 months extension inked into your passport.

All you can do is ask, but I'd bet it'd be a no, because most of the time they send the application to the main office for that area for approval AND it's not uncommon for some approvals to actually take longer than the 30 day under consideration stamps.

Ask at your immigration office BEFORE you apply if the process can be sped up