Well, there are a number of remote server type options available, but if you don't want to run another server, there is a solution I give in one of the above links.
On your slimserver machine you could have a batch file (a BAT) that starts up when the machine is booted up. This file would check every 30 seconds for the existence of a file in a particular folder. If the file is present it starts SlimServer.
Heres an example of the code
REM Checks every 30 seconds for a certain file to exist. If the file exists, it calls an
REM external BAT file, deletes the trigger file and resumes its 30 second check
REM Change the filename to whatever filename you like to check for
REM We use the CALL command as this returns the flow of command back to this script
REM when the BAT file we call has finished
IF NOT EXIST c:\storage\filecheck.txt GOTO SLEEPSECTION
REM There does not seem to be a sleep command avaiable, the following is a hack that
REM emulates a sleep. The number after the n (minus 1) is the number of seconds delay we want
ping -n 31 127.0.0.1>nul
In the above case, the myaction.bat file would actually start Slimserver.
You could easily refine this so that it looks at the content of the 'notification' file and starts/stops/does some other action depending on the contents.
So, in use it would work like this. Your upstairs machine has a shared folder. When you want to start SlimServer you put a file (with a particular name) in this folder. A script running on the upstairs machine sees the file, calls whatever action you want done, and deletes the file.
Would this solution appeal to you?