The closest approach I can think of is this.
1. Make a trigger that fires (does whatever you choose, for instance sets a variable or remembers selections) when the following condition is true:
Selection's Trigger Expression lt_ma is less than X
Name this trigger, for instance, "remembering earlier lt_ma"
2. Make another trigger that does the actual trade with the following conditions:
Selection's Trigger Expression lt_ma is equal or greater than X
and Trigger remembering earlier lt_ma Number of runs per selection is greater than 0
Obviously, if a selection's lt_ma used to be below X and then became X or higher, then it has crossed the target value.