Here is a First sim:

The popcount is applied over 9 bits so it's not possible to prevent simultaneous switching of all 5 wires. But the overall density of transition is clearly decreased: there can not be more than 5 transitions during 2 cycles. Over a longer transaction, this keeps the general EMI spectrum more stable.

That's all can be afforded with only one half of a bit for Transition Reduction, one can't talk about Transition Minimisation at this level, but at least it's something. And it's nice to share the XORs between two bits.