If you are not ready to be played with, stick your finger back through the hole after he does.
One social theorist has described the attraction of this form of sexual encounter thus:
This risk can be reduced through the use of condoms, although their use in glory hole activity is not common.
There are very little talking in public places where gloryholes are often found.
On occasion, the person being played with will want to help you cum.
Some gay men install private glory holes within their residences or other locations they control.
The clearest indicator that you want someone to follow you into a stall or video booth is making an eye contact.
This is the common signal letting the person on the other side know you are ready to receive.
I have never been to one, think people who do are crazy but here you go OP.