you could try putting a thin line of salt along the floor acroos the door ,i doubt they would cross it....cant think of any humane ways though as im sure that may be a bit cruel!
You can buy bucket-type things which you fill with beer or (I think) milk. The slugs are attracted to it, climb in, but can't get out. I'm not sure if the slugs actually die though, in which case emptying the bucket in the morning would be a thankless task - ew..
Get a DVD (or video if you've not succumbed to a �29.99 DVD player from your local post office - why are PO's selling DVD players and toasters? but that's another question not and answer) of Sir David Attenborough's Life On Earth select the deserts episode and play that in your living room; the slugs, believe me, will take one look at it and say blimey its too hot and dry in here for us and leave.
A note of caution if you have any camels in your neighbourhood you could have a bigger problem than the slugs.