So, there are many addons for EU-MJ converters, but all those are either unupdated or have problems, makes me suggest IC² to have an inbuilt one.
It would be a single (or two) block(s)
"Electrical Kinetic Turbine" :
Consumes 4 EU/t to produce 1 MJ/t
Each Overclocker increases EU consumption by 4 and MJ output by 1, transformer upgrades can be used to increase maximum EU/t, alongside battery upgrades for bigger internal buffer
or
Generates 2 EU/t consuming 1 MJ/t
Each overclocker increases MJ consumption by 1 and EU output by 2
Button to change between modes [inverting the energy flow], it is somewhat realistic, if we consider MJ as kinetic/mechanical power.