i have several apps in my menu bar where i do not want to (or need to) see an icon (i prefer an uncluttered menubar on my 13" mbp).
so, for example, i have f.lux (an amazing freebie, that adjusts the display for nighttime viewing); i went into the app package (after quitting it first), and removed the resource file for the menubar...and how have a space.
you could do something like this; perhaps install some minimalist apps that have menu icons, and remove them from the package contents.
not perfect, but it would work. for me...there are spaces but for apps i actually USE>..