[Banknorris]

I have a personal addon that saves bars and also replace macro tabs (general become char macros and char macros become general macros) my solution for this problem is sketched bellow:

--macros whose names are in the format PHxx where xx is between 00 and 99 are reserved for place holder macros
 
local ph_number = 0 --number of current place holder macros
local ph_list = {} --list of place holder macros; k: spell id; v:macro name
local Create_Place_Holder_Macro
 
--put this in the load loop of saved action bars, when you have a spell to this:
--in my version of action bar saver there is no cache, so the code will need some adaptation on this regard
PickupSpell(spell_id)
if GetCursorInfo()==nil then
    if ph_list[spell_id]==nil then
        ph_number = ph_number+1
        ph_list[spell_id] = Create_Place_Holder_Macro(spell_id,ph_number)
    end
    PickupMacro(ph_list[spell_id])
end
 
--put this in the save loop of current action bars, when you have a macro to this to check if you have a place holder macro to save the spell:
if macro_name:match("^PH%d%d$") then
    for k,v in pairs(ph_list) do
        if v==macro_name then
            local actionType = "spell"
            local id = k
            local name, spellRank = GetSpellInfo(id)
            set[actionID] = string.format("%s|%d|%s|%s|%s|%d", actionType, id, "", name, spellRank or "", "")
            break
        end
    end
end
 
function Create_Place_Holder_Macro(spell_id,ph_number)
    local am = GetNumMacros()
    local macro_name = "PH"..string_format("%02d",ph_number)
    local spell_name,_,texture = GetSpellInfo(spell_id)
    if texture then
        if am<MAX_ACCOUNT_MACROS then
            CreateMacro(macro_name,texture,"#showtooltip\n/cast "..spell_name)
            return macro_name
        end
    end
end
 
--you need a way to detect that specialization has changed and when it happens you should delete all place holder macros
local function call_me_when_spec_changes()
    if ph_number>0 then
        for i=1,ph_number do
            local macro_name = "PH"..string_format("%02d",i)
            DeleteMacro(macro_name)
        end
        wipe(ph_list)
        ph_number = 0
    end
end

The basic idea is to put a macro with /cast spell when the spell can't be picked up.