Do I take it that 'bulkhead PIR lights' are not aesthetically acceptable and/or too large - some aren't totally ugly ...I'm amazed nobody makes these things to hardwire. 2nd post in 2 weeks.... Let's get designing!
As for "Let's get designing", conceptually speaking all you really need to do is 'saw off' the 'plug pins' from a plug-in one and attach it to a blank plate. No point in re-designing the whole of the rest of it!
Kind Regards, John
They would be very acceptable if I can find something smallish.