I know it might surprise you, but shocked? Your priest is probably extremely well-intentioned, but the practice really is wrong. The kindest possible thing to do is that which you would do in any other circumstance where a kindly person, even an ‘expert’, has given you advice which, on your perusal of an authoritative source, has proven incorrect–to refrain from taking the incorrect advice.
Suppose your mother tells you to let your teething baby have a ‘bit’ of alcohol (a practice which was even followed by family doctors a couple of generations ago). Would you accept the advice on seeing the Association of Pediatricians giving the practice thumbs down? But you might not feel like telling your mum she’s out of line for the advice which was well-meant and (in a different era) accepted.
Well, it’s the same thing. Just because your priest is a priest doesn’t mean that he won’t make errors. The trick is to accept, “Well, in this matter Father has not yet gotten the memo”, to think that in charity he is doing this and doesn’t know it’s wrong according to the Church’s decision, and then not to immediately assume everything else Father says is ‘wrong’, and (in charity) not to assume everything Father says is right either. (Just like we do with our mums).