try this aproach:
use dummy sprite (blank, invisible)
and set it to create on any touch at touch x and y
than set your events something like this:
on touched sprite + if dummy is overlaping that sprite + set that sprite variable from 0 to 1 = key pressed action
and something like this:
on any touch end + sprite has variable 1 + dummy gets destroyed = key released action
and then return sprite variable to 0