I experimented with using warmed-up mineral oil, mineral spirits or WD-40 to 'liquify' my compound prior to application on the leather. It can work (it DOES, in fact) but, as you've found, it's sort of a messy process. I also realized my tendency was to apply WAY TOO MUCH compound with this method. After all, once it's liquified, it's SO EASY to spread on a nice, thick layer of it. After using the strop for a while, I started using WD-40 on a paper towel to remove much of the excess compound from the leather. To my pleasant surprise, the performance of the strop improved noticably.
I've since re-thunk(?) my method for applying compound. Now, I just 'crayon' the compound onto the leather in a pattern, such as diagonal lines or a cross-hatch pattern with the lines spaced about 1/2" apart. I don't lean into it, just use the weight of the stick to apply LIGHT green stripes. Then, after that, I'll use a paper towel moistened with a little WD-40 to spread it around a bit. This will also remove any excess compound that hasn't embedded itself in the leather (which is OK). For a time, the stripes will still be visible on the leather, which is fine. Periodically, I'll wipe down the leather with a paper towel (usually dry, but occasionally with the WD-40) to clean up the metal residue. I've found the stropping compound to be very effective, when applied minimally in this manner. Also a lot less messy. It will continue to work for a very long time.
