5-position switch in an HH Strat set up for a killswitch

A standard 5-way switch is a simple evolution of the old Strat 3-way switches, which consists of two linked 3-way selectors. The in-between positions just select two of the positions simultaneously, i.e. they put the inputs in parallel. In the standard Fender configuration, one of the linked switches is used only to select the separate tone pots, which may not be all that relevant to you, so you could use that sub-selector as the kill switch by repurposing one of the in-between positions as a short to ground. Just ignoring any tone pots for now (you can wire them independent of the PU selection somehow), and assuming you don't want any coil splitting, you can set up a kill switch for example like this:

Of course, whether you want the kill position on the NeckH + MidS slot or the MidS + BridgeH one is trivial to change.

That said – I wouldn't do it this way. As Tim already commented, it's no problem installing a small dedicated kill switch in the scratch plate, no woodwork needed. Or you could replace one of the tone pots with such a switch. (A pull pot will likely be too slow for the kind of stuff you want to do with a kill switch.)

There's the option of changing a volume pot. for a piggyback type (push/pull). With nothing connected to one position (up or down) it will work as a kill switch - and save any woodwork.