Here's a couple of links that'll get you started with Autohotkey (assuming you're a Windows user):
howtogeek.com/56481/the-begi ... ey-script/
lifehacker.com/316589/turn-any-a ... d-shortcut
Once that's all set up, just drop the code into your main .ahk file (there's a ST syntax file for it from either Package Control or github.com/avi-aryan/AutoHotKey),run it and you're good to go.
I use a slightly different script now, which I use across all my apps - if you want to limit the function of this new script to ST just add it between these lines:
#IfWinActive, ahk_class SKMainWindowClass
Otherwise here's the script (which is triggered by Win + t):
ActiveHwnd := WinExist("A")
WinGetTitle, WindowTitle, ahk_id %ActiveHwnd%
WinGet, ExStyle, ExStyle, ahk_id %ActiveHwnd%
if (ExStyle & 0x8)
Winset, AlwaysOnTop, Toggle, ahk_id %ActiveHwnd%
StringReplace, WindowTitle, WindowTitle, %A_Space%- (Pinned)
if not OnTop
WindowTitle:=WindowTitle . " - (Pinned)"
WinSetTitle, ahk_id %ActiveHwnd%,,%WindowTitle%