utilizing unused ips as a means to block scripted or physical hacking attempts

ok, i have 20 ips delegated to a server

only 5 ips are utilized by server

the remaining are just sitting there


those attempting attacks will go through the list

they hit the first ips then go through the list

modsec is not blocking subsequent attempts at ip attacks until they are attempted

thus, 000.001 is hit and denied

then 000.002 is hit and denied

by same incoming ip

below are 3 of 14 attempts by one ip as shown in modsec

124.219.58.77 7x.53.xxx.xx0
124.219.58.77 7x.53.xxx.xx1
124.219.58.77 7x.53.xxx.xx2

so, the ip 124.219.58.77 is going down ip list. x hundreds

i want to tie each unused ip or all unused ip's to a web page or program that immediately blocks the ip.

though i could remove the ips i see them as a way to "*midway" these attackers
[*ambush]

having a means to stop on first ip would completely block attacker to any access for a period of time

especially the scripted Asian attacks

any comments pro or con appreciated.

i have most security packages installed so if i am missing the facts of using them to do this will also be appreciated

rock

- - - Updated - - -

what i would like to do is similar to this how to except i need it automated.

Nullroute IP using route command

Suppose that bad IP is 65.21.34.4, type following command at shell:

# route add 65.21.34.4 gw 127.0.0.1 lo

You can verify it with following command:
# netstat -nr
OR
# route -n
You can also use reject target (thanks to Gabriele):
# route add -host IP-ADDRESS reject
# route add -host 64.1.2.3 reject

To confirm the null routing status, use ip command as follows:
# ip route get 64.1.2.3
Output:

RTNETLINK answers: Network is unreachable

Drop entire subnet 192.67.16.0/24:
# route add -net 192.67.16.0/24 gw 127.0.0.1 lo