Electroporation of one-cell embryo?
The buffers are usually supplied with the electroporation instrument; at least Lonza provides buffers for different types of cells. Single cell electroporation techniques exist, but they have been mostly done on neurons.[1,2]

You can also try microinjection but it requires some practice. This study reports a transfection agent called VisuFect which can be used for zygotes as well.

I am not very sure about the success rate (AFAIK it is not that good) but I think it is anyway risky with organisms which do not produce a lot of embryos.