Bah .. sometimes the right Google query answers the question. Those curious we can make them with a WMI query:
$Arguments = @{Name = $Name;Description = $Description;PkgSourceFlag = 2;PkgSourcePath = $Source}
Set-WmiInstance -Namespace "Root\SMS\Site_$SiteCode" -Class SMS_SoftwareUpdatesPackage -Arguments $Arguments -ComputerName $SiteServer -ErrorAction STOP
In the above string I'm using variables for Name, Description, and Source Directory, as well as Site Server and site code. Now I just have to distribute that package and I'm good to go. Home stretch here I come!