For anyone looking back at this post, the latest verison of the Make Me a Route feature now has a "Walking" option, which should give a higher preference to paths than the previous version.
Thanks for the feedback. There isn't currently an option to bias routes to use footpaths with the Make Me a Route feature, but we are hoping to introduce some enhancements to this feature in the near future, so will certainly investigate whether this is possible.
Although I pre-selected walking, the auto-route function seems to prefer roads to paths (even if avoid highways is selected). Is there any way, short of doing it manually, so have it prefgers paths?