This is possible. Make an brush entity info_notnull with the following fields

touch multi_touch
wait -1
targetname trig
use InitTrigger
target event

This trigger will not be spawned until trig is targetted. From then on it will act like a trigger_multiple when touched, although things like shootable triggers or triggering by targetting(like a trigger relay) will not. You can add all the usual fields like wait time. If you want sounds, you can't set the sounds field like usual, but if you set noise to the sound you want, it'll work assuming something else precached it.

You can probably adapt this to work for other kinds of trigger as well, not sure exactly which are possible though.