Windows – Domain member as ntp server for other (non-domain) network

I am attempting to synchronize the date and time for a number of computers belonging to a non-domain, statically configured network (e.g. computer B in illustration) with a node which is residing in a domain on a different network interface (A).

Despite my efforts, I am unable to make synchronization happen 🙁

A:   10.0.0.A / 172.64.0.A   Windows 2008 Server (32bit)
B:   10.0.0.B                Windows 7

So far, I have tried to enable the NTP Server on A through different variations on this idea:

C:\> w32tm /config /reliable:yes
C:\> w32tm /config /update
C:\> net stop w32time
HKLM\SYSTEM\CurrentControlSet\Services\W32Time\Config -> AnnounceFlags = 0x5 (or 0xA)
HKLM\SYSTEM\CurrentControlSet\Services\W32Time\TimeProviders\NTPServer -> Enabled = 1
C:\> net start w32time

On B, I have tried variations on the following:

C:\> w32tm /config /syncfromflags:manual /manualpeerlist:10.0.0.A
The command completed successfully.
C:\> w32tm /config /update
The command completed successfully.
C:\> net stop w32time
C:\> net start w32time
C:\> w32tm /resync
Sending resync command to local computer
The computer did not resync because no time data was available.

I have also attempted to make do the configurations on A and B through local group policy on the machines in question, with no result.

(edit) Restrictions: The two networks are completely separate, except for A and a few workstations connected to both. Otherwise, the static network on the right is completely isolated from the world (it is a thin client network). Any topology changes are unfortunately out of the question at this point.

I am willing to look at possible workarounds, and on-the-second accuracy is not a major concern to me (+-30 seconds is ok). I'd very much prefer to avoid 3rd party software. One workaround I have attempted is to have a logon Powershell script on B read the time on A, but that has its own problems, possibly for another thread.