The only thing I can think of for you would be to change it at the registry level. Note that I'm not recommending you mess with the registry, but this does do what you want -
The default directory for a new profile is determined by the ProfilesDirectory in HKLM:\Software\Microsoft\Windows NT\CurrentVersion\ProfileList, and by default is %SystemDrive%\Users, changing it to $userpath should do what you want -
$regpath = "HKLM:\Software\Microsoft\Windows NT\CurrentVersion\ProfileList"
$regname = "ProfilesDirectory"
set-itemproperty -path $regpath -name $regname -value $userpath
Hope that helps!