Specifying SD card mount options upon boot
Urukdroid has a special script, /system/bin/mount_sdcard.sh, that mounts the SD card upon boot. This script understands (V)FAT and EXT4. Anything else is left to the vold automounter. Archos modded vold so it could do a bit more than stock A 2.1 vold, e.g., mount EXT3 file systems.

I upgraded the file system on the SD card to EXT4, and now mount_sdcard.sh mounts the SD card upon boot with the correct mount options.

Thanks to $aur0n for helping me solve this.

Upgrading an EXT2 or EXT3 file system to EXT4 is easy, see https://ext4.wiki.kernel.org/index.php/Ext4_Howto#Converting_an_ext3_filesystem_to_ext4 .