If you want a knot that will not take up much space, run the halyard through whatever you are tieing, then tie a simple square knot in the very end of the halyard on it's own. Then tie the halyard back around itself with a figure eight. You can substitute another square knot for the figure eight (it will be slightly smaller) but it will be more difficult to undo later.

I have a spinnaker that uses ALL the available hoist height and I've been tieing the clew and head this way for a while.