The AME must and will do the prone ECG as necessary. The stress ECG is another matter and is really quite fun as long as you don't weaken.
Both in the UK and in SA for a Class I medical, I have always found that a stress ECG, completed by a cardiologist and within the appropriate licence medical validity period, has always been accepted respectively by both the UK and the SA CAA medical departments. In fact my UK AME doesn't have a stress ECG machine anyway. In the case of doubt, he'd refer to a cardiologist which means, in the UK, that you'd have to go private and pay top dollar. It all depends, of course, upon what sort of medical insurance you have too.
Now back in the old days in SA when medicals were done at the Military Medical Institute (MMI), the pilot candidate was examined by a troupe of trainee doctors. As a consequence of this, results were varied and it was quite often that specialist reports were requested. Once you've had a report requested, that fact goes onto your medical record and as matter of self defence it sometimes behove the returning Class I medical candidate to summit another report at the time of the next medical in order simply to get the doctors off his back. A couple of years at
PR in med school would have done many of these young jackanape quacks a lot of good.
As for my BP and thank you for the commiseration, but since the last transplant it's been stuck nicely on 117/59 which ain't bad for 80!