This article provides some useful ways of remapping keys, here are some useful tidbits from the article:
Sharpkeys:
SharpKeys is a program that’s brimming with features. It’s a keyboard
remapper that offers an easy-to-use interface. All keyboard remaps are
saved permanently, when using SharpKeys, since it adds values to the
appropriate registries. A restart of the computer is required for
keyboard changes to take effect.
Keymapper:
Thanks to its large keyboard graphic, Key Mapper is one of the easiest
key remappers you can use. When using this tool, the keyboard graphic
will take up most of your screen, making it easy to see.
As mentioned in the article, make a system restore point first, so you don't lose everything if something goes wrong.
Enjoy your keymapping!
Edit: The IBM website provides useful info on key mapping that should help you out.
Keyboard remapping lets you associate a sequence of keystrokes with a
particular action, so that typing the sequence of keystrokes causes
the action to occur. The sequence of keystrokes can be either a single
key or a single key combined with Shift, Ctrl, or Alt. The action can
be to display a character, to execute a host function, to execute a
custom function, or to execute a menu command.
Autohotkey is a good resource as well, Apparently it can do multi-key combinations. According to this question, it can
[...] map key sequences, macros, mouse input, pretty much anything to
a keypress or key combo.
And this question gives some more details and resources.
If you can't get it to do a full winkey+shift+s function, maybe have it do winkey+shift, and press "S" yourself?