Vista - Real nested Powershell interpreter

Hi Together

I try to make an extended Interpreter for my personal Administration
to load some global Methods and execute them as i need.

I did so far created a script with the following content. (just typed
from mind, maybe no working as except)

#scriptname start.ps1

function global:getsubdirs()
{
params(
$folder = 'c:\'
)
}

$loopingplease = $true

while($loopingplease)
{

$command = Read-host "Type Command:"
if($command -eq "exit")
{
$loopingplease = $false

}
else
{
Invoke-Expression $command
}
}

##End of Script

Know when i execute a long running "Invoke-expression" and stop it
with CTRL-C i goes directly to the Base Powershell Command Prompt.

But will still stay in my own prompt.

Is it possible to do?

Thanks in Advance.
Ivo Looser