How can i override variable value only for a host via extra-vars supplied through command line

[ishan jain]

Suppose i have this var defined in my inventory file:

[group10

host1

host2

host3

[group1:vars]

source=/opt/config/

And my target hosts are a group of 3 or more servers. Now while invoking the playbook, i would like to override the value of 'source' variable only for a single host, say host2. Which inbuilt hostvar should i override for this ?