is it possible to skip mounting errors during boot?

i have 3 usb disks and for them entries in the fstab.
when they are connected there is no problem during boot, but if one of them is disconnected the boot stops with a purple screen and says that the disk coul not be mounted.

the problem is that the boot stops there until u press s to skip it and cannot login per ssh

karmic booted with these errors and just didnt mount this disk

thank you for help