I'll take a stab at this answer. The OP did not say what OS is being used, so I will be somewhat generic.
First, make a file called free_os_cache.sh

#!/bin/sh
# Description
# Forces the OS to clear OS caches

# Run a sync to reduce dirty caches
sync

# Tell the OS to not make warnings
echo 4 | tee /proc/sys/vm/drop_caches

# Tell the OS to clear caches
echo 3 | tee /proc/sys/vm/drop_caches

# Wait a tiny bit, just for safety (may not be necessary)
sleep 5

# Reset to 0
echo 0 | tee /proc/sys/vm/drop_caches

exit

Then, allow it to be executed
chmod 744 free_os_cache.sh

Next, add this to your sudoers file:
ALL = /path_to_file/free_os_cache.sh

Now, your users ought to be able to run this command:
sudo /path_to_file/free_os_cache.sh

That ought to get you close enough that you can tweak it for your particular environment.
$0.02

I'll take a stab at this answer. The OP did not say what OS is being used, so I will be somewhat generic.
First, make a file called free_os_cache.sh

#!/bin/sh
# Description
# Forces the OS to clear OS caches

# Run a sync to reduce dirty caches
sync

# Tell the OS to not make warnings
echo 4 | tee /proc/sys/vm/drop_caches

# Tell the OS to clear caches
echo 3 | tee /proc/sys/vm/drop_caches

# Wait a tiny bit, just for safety (may not be necessary)
sleep 5

# Reset to 0
echo 0 | tee /proc/sys/vm/drop_caches

exit

Then, allow it to be executed
chmod 755 free_os_cache.sh

Next, add this to your sudoers file:
ALL = /path_to_file/free_os_cache.sh

Now, your users ought to be able to run this command:
sudo /path_to_file/free_os_cache.sh

That ought to get you close enough that you can tweak it for your particular environment.
$0.02