Sounds like you plan to cleat the outhaul on the boom – as opposed to running dual control lines aft to the centre thwart which is how a racing boat would be fitted.
There is quite a useful discussion here which if you have not seen is worth studying carefully;
http://wayfarer.org.uk/forum/viewtopic.php?t=580&highlight=outhaul
In the photo the white line is the boom outhaul, there is a small slot cut/drilled for the line to exit in front of the clamcleat. This was done by the rigger who supplied the spars – so they would have had the right tools for the job. You don’t need to worry too much about the line rubbing as it exits the boom section as the movement is quite small. Perhaps drill a line of holes close enough to make an oval and then file out to get a smooth oval – about 25x10mm should be enough. But you may have other tools that are better suited to cut this.
I added a couple of photos to show how the line routes, and the slot cut in the underside of the boom.
Perhaps Swiebertje’s arrangement is better – less friction with one less block.
Hope that helps