The commandline to do this is:
regedit -s DNS_suffix.reg

where DNS_suffix.reg is

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters
+]
"SearchList"="yourdom.com new.yourdom.com test.yourdom.com"
[download]

Depending on how many systems - just use a system call.