First, this is something that has to be dealt with at the AD and administration level of your schools.
If you're playing six-man football, you're doing it because of low numbers.
If you had big numbers, you'd be playing 11 man football, maybe cross country in the fall, basketball and soccer in the winter, baseball, track, golf, tennis and maybe even power lifting in the spring and you'd have enough bodies for each of them.
You have to look at your athletics as a program, not an individual sport. My old line was that we had only one team at our school ... the sport only changes.
Let's face it. Most of our kids aren't going to be sought after for D-1 scholarships in most sports (although, Coach, I remember one of your school's basketball coaches convincing a young man to transfer from my school to yours several years ago and promising him that the kid would get a basketball scholarship to Duke University...seems I missed that article in the paper about the kid's scholarship). Even D-2 or D-3 college teams are difficult to make at the small school level. I've seen "all-state" small private school players struggle to be the last kid on the bench in college sports. Yes, some have done well, but it's the exception to the rule.
This malarkey about "I'm saving myself for basketball (or baseball, I've heard that one the other day from another school) is some kid and his daddy overestimating the kid's value to the game. And maybe some roundball coach who thinks Coach K would be calling him for advice if Coach K had his phone number on speed-dial.
First, you should not start your basketball season until football season ends. That means, if the last football game (week 10) is Nov. 1, start buckets practice on Nov. 2. I never scheduled basketball games until Thanksgiving week and I told schools I scheduled that games those first couple weeks were dependent on the football team not playing. Coach is gonna scream bloody murder, but that's why you have an Athletic Director to provide direction to your program. (And hey, this plays all ways. If basketball season starts to infringe on spring sports due to playoffs, then those sports just have to wait.)
I expected kids to play football in the fall and basketball in the spring; girls were expected to do volleyball and basketball. Sadly, in the six or seven years since I left as Athletic Director, that rule has been pretty well tossed out the door.
But I'll tell you a story from our second year of football. We had two guys (a senior and a freshman) who were "saving themselves for basketball." We had 8 guys out for football, and there were four boys not playing football (including those two).
I pointed out to each of those two young men that yes, we can play six-man football with eight guys. But if those eight guys had the same opinion about basketball, then there are only four to start playing five-man basketball ... the two of you, another young man who would play basketball (but had medical issues that prevented him from being cleared for football), and a young man who was, shall we say, the music nerd who was never going to play any sport. Under the rules, I can't start a five-man basketball game with four players.
There are guys who are going to help you with your sport -- maybe in this case, it's basketball -- if you help them with their sport -- football. And those are the true lessons of participating in sport at this level ... building friendships, working together towards a goal. You know, like the NCAA ad, most of our athletes are going pro in something other than sports.
By the end of the week, I am proud to report, we had a roster of 10 for football.