How to interact with remote machine outside of a session? - powershell

Question

I'd like to install software on some of my domain computers silently. Since these software packages don't come in the form of an MSI, I thought I'll try to do it using Powershell.
In a first step, I set up Powershell remoting. The following command works:
PS $ Test-WSMan -ComputerName rmtComputer
wsmid : http://schemas.dmtf.org/wbem/wsman/identity/1/wsmanidentity.xsd
ProtocolVersion : http://schemas.dmtf.org/wbem/wsman/1/wsman.xsd
ProductVendor : Microsoft Corporation
ProductVersion : OS: 0.0.0 SP: 0.0 Stack: 3.0
The software packages to be installed are on network shares. Unfortunately, it doesn't seem possible to start these install files directly. As Kevin Marquette explains in his article on Powershell, this is due to some double hop credential problem. The solution is to first copy the setup file from the share to a local folder, then start the setup.
In the same article, he shows 2 ways of doing that. The first way looks as follows:
Copy-Item -Path $file -Destination "\\$computername\c$\windows\temp\installer.exe"
Invoke-Command -ComputerName $computerName -ScriptBlock {
c:\windows\temp\installer.exe /silent
}
Neither of these 2 commands works for me. Running the copy-item command returns The network path was not found. I can confirm that both the computer as well as the user have read access to the respective share.
Running the invoke-command command doesn't return any errors but nothing happens on the computer in question.
Marquette goes on to describe another way of doing the same, using a Remote Session:
$session = New-PSSession -ComputerName $computerName
Copy-Item -Path $file -ToSession $session -Destination 'c:\windows\temp\installer.exe'
Invoke-Command -Session $session -ScriptBlock {
c:\windows\temp\installer.exe /silent
}
Remove-PSSession $session
This, on the other hand, works perfectly. Any hint you can give me as to why this works but the other way doesn't?