yeah, i had one. take out the bolts and folding parts, put some other nuts and bolts in the holes, drill a hole through the headtube and "walls" and presto, there you have it. at least thats how i did it.
If its an old a2 (square deck) goto the scooter modding super thread and watch the how to lock a folding mech video, its done on a B but its basically the same on an A. If you have a new A someone else might want to help you, i don't really know the popular ways of how to lock them.