I've top-worked a couple of trees on my farm without waiting for new shoots. My success was around 30% on approximately 20 grafts. Here's how we did it:
We cut the scion the same as we would for a cleft/wedge graft. On the rootstock, we made two vertical cuts through the bark. We lifted the bark, inserted the scion, and wrapped the wound as tight as we could with old tire rubber.
In hindsight, to improve our success, we should have put three or four scions on the above branch, then wrapped.
A similar method was good when the rootstocks of my young trees were too thick for cleft grafting.
I prefer cleft grafting in part because they are so strong. Birds can land on them without concern. The bark/veneer grafts must be wrapped well to prevent accidental movement of the scion.
As with any mango grafting, for best results the rootstock must be in a growth flush and the scion buds swollen, ready for their growth spurt.