I am SURE there is a better way to do this, but I don't know much in the way of programming languages, so this is how I did it with a batch file and standard Windows tools.

The Machine SID will be inserted into the Registry so LANDesk can pick it up with the next inventory scan.

I wrapped PSGETSID.EXE and the .BAT file into a Self-Extracting EXE (WinRAR).  It extracts to %TEMP% so no files get left behind when it's done.

Contents of BAT file:

@ECHO OFF
psgetsid -accepteula > .\GOTSID.TXT
findstr /v "SID FOR" .\GOTSID.TXT > .\MYSID.TXT
set /P MACHINE_SID=<.\MYSID.TXT
reg add "HKLM\Software\Intel\LANDesk\Inventory\Custom Fields" /v MACHINE_SID /t REG_SZ /d %MACHINE_SID% /f