you can achive this through policy map and policing
make an access-list that either match any traffic to from any source to your server
or a spisific traffic from spisific client to your server in this case u have to creat an ACL for each client
then make a class maps matching that ACL or ACLS
then for each customer make a policy map
and first class in this policy is the map that u have created matching the traffic destined to ur server and make the rate limit
such as police CIR to 4Mbps
then make and apply another class map that match you clent internet traffic which mostly any to any or u can make it class-default to match any traffic then police the trffic to the amount you want for each customer
you can make policy map for each customer if you have saperate interface to each or combine the class map in one policy if you have one interface with them but you have to be more spisific in your calss maps in this case
if you want more details or commmand let me know
there is other way u can do it called nested Policy map
but try the above one better
by the way u can do the above policing on L3 switches aswell!
good luck and rate if usefull
