Rockler( and other woodworking supply companies---WoodCraft, for instance) sells a glue syringe---to inject glue in very small places---ideal for your situation.

Better than that is "Chair Doctor" glue. Woodcraft and Lee Valley both carry it. It's very thin and wicks into the joint, swells it up and glues it down. It is _not_ the same thing as Chair Loc. I use it whenever I can't get into a joint easily (for example some yahoo has filled it full of nails or staples.)

If that fails, I drill out the wedge, remove the spindle/arm, clean up the joint, reglue it, and put in a new wedge. This is much easier (and more common) for wedges on the bottom than on the top (for example holding legs on a Windsor chair with through tenons).

Here is a link that might be useful: chair doctor glue