In batch how to find registry key name with partial name?

I need to export specific reg key from the windows registry in batch :

reg export "HKEY_USERS\S-1-5-21-662932327-638391458-17307956-1000\Software\somesoft" %pathtemp1%\export.reg /y

the problem is that depending on the machine that I install the key name value varies :

S-1-5-21-662932327-638391458-17307956-1000

S-1-5-21-625306749-2316130166-4004245817-1000

So how i can make do this :

S-1-5-21-*-1000

On windows 7 pro x64.

Can you give me an example ?

Thanks.