Have a pediatric neurosurgeon come and do a presentation on TBIs for the football team parents.
I knew a guy who built a really solid girls team just by sending home flyers listing all the kids on the team over the years who got college scholarships to run XC/track. It was just a handful, but parents flipped out and pushed their kids to join. Doesn't work for boys as scholarships are rare these days for distance boys.
Otherwise, I think middle school is where you build your program. By the time they get to high school, they have bought into whatever the sports culture is at the school and are very difficult to move. Schools that have low XC/track numbers are usually either schools where sports are not a big deal and kids don't really care much about getting a letter jacket, etc. or are schools where the big team sports are huge and everyone looks down on the distance runners. But if you are doing a good job getting kids interested when they are in middle school, the team will pretty much build itself in high school. Middle school kids are more likely to join as freshmen because they want to have a social circle and be part of something as soon as they hit high school.