; as a new modifier key

I want ; to be a new modifier key. The following works almost perfectly.

`;::
if GetKeyState("LShift", "P")
    Send `:
else
    Send `;
return

`; & x::
if GetKeyState("LShift", "P")
    ...
else
    ...
return

Only point 2. of the following wishlist does not work. Does anybody know how to fix this code?

1. ; to be ; when pressed alone
2. shift ; to be : when pressed alone
3. ; with x to be the second ...
4. shift with ; with x to be the first ...

The following works perfectly, but is ugly code due to code duplication. Maybe cleaner code is possible.

started := 0
LShift & `;::
if started = 0
    started := A_TickCount
return
`;::
if started = 0
    started := A_TickCount
return

LShift & `; Up::
if A_TickCount - started < 500
    Send `:
started = 0
return

`; Up::
if A_TickCount - started < 500
    Send `;
started = 0
return

`; & x::
started = 0 ; <==== !
if GetKeyState("LShift", "P")
    ...
else
    ...
return

The key ; now works as modifier key whenever it is used in a combination with x (without delay) or if it is pressed more than half a second. The delay is not neccesary and can be removed; it's just there prevent misinterpretation of an accidental modifier keypress as a ;. The colon : works correctly too.