SleepWatcher uses Unix executables placed in your Home directory. It is totally different from Automator scripts or Startup items, though the command lines are almost identical (this is why I made a mistake in my previous post by telling you that I "used the same script with SleepWatcher", sorry

).
I use SMC Fan Control to get to the MacBook Air's SMC settings, so the command line only works with this method. I actually don't use the application itself and the following method is still worth a reading even if you are using a different method to access the SMC settings (you will just have to change the path of the command line).
To create such an executable, open textedit and type :
#!/bin/bash
And on the next line the script you would like to execute.
It gives me :
#!/bin/bash
/Applications/smcFanControl.app/Contents/Resources/smc -k F0Mx -w 2710
Same line as in Automator (to set the maximum fan speed at 2500 rpm).
Then, still in textedit, open the menu "format" and clic on "convert to text file". You should see now a very ugly kind of font (perfectly normal

).
Save your text in your Home directory (not elsewhere) as ".wakeup" (with the dot but without the quotation marks). You cannot call it differently (that's the way Sleepwatcher works). Because it has been saved with a dot before the actual name, it is considered a hidden file. It is not necessary to reveal it but if you really want to feel secure use a software to reveal hidden files (I personally use Onyx).
Now open the Terminal and type :
chmod +x /Users/YOURHOMEDIRECTORY'SNAME/.wakeup
of course change YOURHOMEDIRECTORY'SNAME into your home directory's name

.
Normally the text file is now a Unix executable and has a totally new and much better looking icon.
Please tell me if there is any mistake here, I'll correct them as soon as possible.