disable static ip that no one can use that static ip ?

Hello to all respected expert,
   actually my company got a lease line connection of internet . we have three organization org1,org2 and org3 in one city all organization have their own lease line connection. all organization bound together by wireless network .Now I am working in org1 the ISP providers us 15 static ip with lease line connection. We have use only 4 ip from that and other 11 ips are free . Now I want that 11 ip could not be use in org2 and org3. i.e. any cannot use these static ips.how to disable these ips to ping. please help me it is very urgent for me.


Thanks