I use a lot of scent in tubes. I wrap a few turns of pipe cleaner around the hook shank behind the head. The fibers hold the scent better and its buried in the tube. For Lake Michigan I use a lot of the Pro Cure Sticky Gels in Smelt or Alewife. For bass I have done well with Smelly Jelly "Bass Feast" which is garlic and crawfish.
I've packed tubes with squid or a pinch of canned mackerel which works very well on Lake Michigan, but its a mess to deal with.
I wonder if you could reduce coffee down to a thicker consistency and squirt it into tubes?
Marc