Actually, I was using the right syntax, I accidentally wrote it wrong here.
Anyway, here's my config:
console=tty0
panic=10
loglevel=3
extraargs=disp.screen0_output_mode=EDID:1680x1050p60 hdmi.audio=EDID:0 nozswap nortc host=WebServer restore=mmcblk0p2 home=mmcblk0p2 tce=mmcblk0p2 opt=mmcblk0p2
If I add anything here it will boot with default Tiny Core settings and won't use any of mine.
Also, how to change the resolution to 1680x1050 because my setting seems not to work. The picture is cropped out and the monitor doesn't always show the picture, so I'm guessing that it's using 1080p instead of 1680x1050.
Moreover, if anyone is interested, I built a standalone lighttpd 1.4.32 + PHP 5.4.16 with all the libs they need (at least I think so, someone could test this more thorougly, it suits my needs so I didn't) and packed it in a tcz. Because it's somewhere between a scm and a tcz, I guess I can't submit it to the official repo. I wasn't sattisfied with BerryWebServer from berryboot so I built my own.