How can you not issue commands in DSL? Are you trying to install or run?
toms has vi. If DSL is already installed, mount the root partition and 'vi /mnt/whatever/etc/fstab' - arrow down or hit 'j' a few times, hit '$' if you don't have a blank line and 'a' or just 'i' if you have a blank line - type Tink's line (modify for your partition), hit 'escape', and ':wq'.
If you're trying to install, there's a way to initialize the swap at the boot prompt, I believe, but I forget how. Maybe somebody can say or you can find that info. Don't the DSL install docs say?