CloudFlare page rule or similar to a custom internal URL with the max request timeout jacked up as high as possible (or whatever) set, stick a little async web server behind it that hangs every request after the first byte for say.. 1 hour. Give the aync web server a good chunk of RAM to waste. Most providers don't bill for time, only bytes, and most bots have some timeout tolerance, especially when the status headers and body are already being sent
Similarly, you can also try delivering one byte every 10 seconds or 30 seconds or whatever keeps the client on the other end hanging around for without hitting an internal timeout.
for char in itertools.repeat(b"FUCKOFF"):
await resp.send(char)
await resp.flush()
await asyncio.sleep(10)
# etc