How can I add a sql user as a sysadmin during SQL Server 2016 Express installation?

I'm trying to find a way to add a sql sysadmin user when I install Microsoft SQL Server 2016 Express.

Currently I use the following command line syntax to install SQL Server...

SQLEXPR_x64_ENU.exe /QS /ACTION=Install /FEATURES=SQL
     /INSTANCENAME=SQL2016EXPRESS /AGTSVCACCOUNT=sqlagent
     /AGTSVCPASSWORD={PASSWORD} /AGTSVCSTARTUPTYPE=Automatic
     /SQLSVCACCOUNT=sqldbengine /SQLSVCPASSWORD={PASSWORD}
     /SECURITYMODE=SQL /SAPWD={PASSWORD} /ADDCURRENTUSERASSQLADMIN
     /IACCEPTSQLSERVERLICENSETERMS /IACCEPTROPENLICENSETERMS

I was hoping there was some type of way to do this with a switch (such as /SQLSYSADMINACCOUNTS).  Unfortunately from what I can tell the switch /SQLSYSADMINACCOUNTS only deals with Windows accounts and NOT SQL accounts.

Is there any way to accomplish my goal while I'm installing SQL Server?

List of install switches documented on MSDN

Arvo Bowen III