Scripts do not allow the ability to transfer files.
You'd need to issue commands to something in order to do the copy.
Examples of methods:
Initiating a VPN connection then transferring from a fileshare.
Initiating an FTP download (Something like this: FTP through PowerShell )
Using an already available file transfer utility like SCP.
You can use the custom package option (One2Many Task). It will download all files you upload to the task. If you use a PowerShell script, you can refer to the random directory LMI puts the files in through the variable $PSScriptRoot as the script will be in the same directory.
#Rudimentary example
#Uninstall old products since they cause new installations to abort
(Get-WmiObject -Class Win32_Product | Where-Object { $_.Name -match 'Awesome Program'}).Uninstall()
#Start Install
Start-Process -Wait msiexec -ArgumentList "/i $PSScriptRoot\AwesomeProgram.msi TRANSFORMS=$PSScriptRoot\AwesomeProgramTransform.mst"
#Install dependent program
Start-Process -Wait msiexec -ArgumentList "/i $PSScriptRoot\DependentProgram.msi"
#Install second dependent program
Start-Process -Wait msiexec -ArgumentList "/i $PSScriptRoot\AnotherDependentAwesomeProgram.msi"
#License the program
Copy-Item -Path $PSScriptRoot\AwesomeLicense.lic -Destination "C:\Program Files (x86)\AwesomeProgram\LicenseFile.lic" -Force