I see, he wants to ping some device and force the check_ping plugin to use both of his network cards. Of course, this would take 2 checks.
To do this, it appears you would have to modify the source code for the check_ping plugin. The file is the check_ping.c file. Modify it if you can, and make it use the -I switch for the /bin/ping command.
Right now, the check performs something like this command:
/bin/ping -n -U -c 5 localhost
I don't know how to modify the source since I"m not a hacker, but you would add the -I to the source and then recompile the file. Give it a different name like check_ping2