OK thanks. I can see that on the surface, this is not possible.
However as a workaround, is it possible to assign the date and time of the last trade/alert to a variable and also assign the date and time of the next MA cross to a variable, and then issue a condition that says:
If Time of Last Sell Trade (ie VarSell) < TIme of MA cross (ie VarCross), then open a sell trade. If not, do nothing?
This way, the EA will keep checking every tick for the next MA cross. Once this is found, it will compare the time of cross with the time of the last trade and then place a trade. However if it does not find an MA cross, no trade will be opened.
If the above is not possible, then I guess I would have to give up 
Regards