"Customise My Trip" seems to be the trick!

Search for that for flights+hotel to Madrid with "Multiple hotels" picked. On the hotels screen, the places search box knows about more places! I can then pick where I'm going there, check in and check out dates matching the flights, don't add another hotel, then get prices.

It only shows about a quarter of the number of hotels that Expedia or similar shows for a hotel-only booking for my destination, but it does work out a fair bit cheaper than CE flight+hire car to Madrid plus separate hotel booking

(I tried with Expedia, it only gave silly+expensive 1-stop options involving a small regional airport, I couldn't get it to just fly me to Madrid and offer hotels where I'm going)