I'm sure you tried but the definitive option would be a BIOS switch to change it. Sometimes is says S3, sometimes it says Linux sleep (like my personal ThinkPad)
But if you don't have that toggle at all, the firmware probably dumped S3 entirely - especially if it's a relatively new machine and you'll have to lean much more on Hibernate like my new work ThinkPad.
I would investigate whether an older BIOS version still has the S3 toggle since some BIOS updates have removed S3 I believe but a search of forums would probably turn up enough complaints to hit your radar.