Super difficult situation, as you know.
First piece of advice would be to get good at "group" sessions.
Example:
When we are playing a spread second exchange team we have a session of practice called "diamond drill." In this drill we do not have receivers on the offense. We play with two upbacks and one spread back (3 total players) vs 2 DL and 1-2 LBs. (3-4 players). From there we would simulate actions the offense will do and we coach our defense on their technique / responsibility.
This allows you to get true game like reps with less people than 6v6.
You could then flip and only play DBs vs WRs and a Q, we call that pass skelly.
Example 2:
When we were an undermanned 11 man team we would do a fair amount of "half line."
We could play a LT and LG vs 2 DL and a LB for example. Good opportunity to coach both sides of the ball.
You could adjust this for your offense. For example we are a tight team, if we wanted to we could play with a TE/RB/FB vs a DL/LB/Corner.
Separate ideas:
- Using coaches for scout team QB/SB can be a good idea. Find a young alumni and have him run around to give your defense a look.
- Utilizing circuits even with a small group is a good way to work universal techniques. One coach is running a tackling drill and another coach is working a block destruction drill for example.