You can still change this, but the lovely folks at PayPal have buried it even deeper, in an area where it doesn't belong.

...and you can't change it from eBay's checkout anymore, which is ridiculous. You have to back out of checkout and go back in once you change the setting on PayPal's site.

Go to your profile (the gear), payments, preapproved payments, then click "set available funding sources". By any source that's a credit card, there should be a "conversion options" link where you can select "bill me in the currency listed on the seller's invoice"

When set there, the DCC declination applies across all PayPal transactions. I just bought something from the UK off eBay the other day and it correctly defaulted to charging my card in GBP rather than using whatever insane GBP -> USD rate I'm sure PayPal is using.