With setaudit it is possible to specify audit configurations on a process directly at the runtime.
All audit events are redirected to the auditd(8), an audit log management daemon.
setaudit [-46] [-a auid] [-m mask] [-s source] [-p port] command ...
Example of enabling all exe related audit events performed by a command and its child processes:
setaudit -m ex command
setaudit can be found in the FreeBSD Ports under security/setaudit:
pkg install security/setaudit
cd /usr/ports/security/setaudit/ && make install clean