WSUS clients actually do a pull. On the clients, you may have to do a run: gpupdate /force (done from cmd box and may require a reboot) and wuauclt.exe /detectnow. The GPupdate and changing the client local registry should do the trick.
You might even have to update the client registry (deliver the .reg through AD) with something like this (local):
Windows Registry Editor Version 5.00
[HKEY_LOCAL_MACHINE\SOFTWA
RE]
[HKEY_LOCAL_MACHINE\SOFTWA
RE\Policie
s]
[HKEY_LOCAL_MACHINE\SOFTWA
RE\Policie
s\Microsof
t]
[HKEY_LOCAL_MACHINE\SOFTWA
RE\Policie
s\Microsof
t\Windows]
[HKEY_LOCAL_MACHINE\SOFTWA
RE\Policie
s\Microsof
t\Windows\
WindowsUpd
ate]
"WUServer"="
http://your server name here"
"WUStatusServer"="
http://your server name here"
[HKEY_LOCAL_MACHINE\SOFTWA
RE\Policie
s\Microsof
t\Windows\
WindowsUpd
ate\AU]
"AUOptions"=dword:00000004
"AutoInstallMinorUpdates"=
dword:0000
0001
"DetectionFrequency"=dword
:00000003
"DetectionFrequencyEnabled
"=dword:00
000001
"NoAutoRebootWithLoggedOnU
sers"=dwor
d:00000001
"NoAutoUpdate"=dword:00000
000
"RebootRelaunchTimeout"=dw
ord:000004
80
"RebootRelaunchTimeoutEnab
led"=dword
:00000001
"RebootWarningTimeout"=dwo
rd:0000003
0
"RebootWarningTimeoutEnabl
ed"=dword:
00000001
"RescheduleWaitTime"=dword
:00000010
"RescheduleWaitTimeEnabled
"=dword:00
000001
"ScheduledInstallDay"=dwor
d:00000000
"ScheduledInstallTime"=dwo
rd:0000001
1
"UseWUServer"=dword:000000
01