I configured it through the interface and left the API URL untouched (so it's http://explorer.litecoin.net/chain/Litecoin/q).
However, when I request an update it fails, and when I look into the logs I can see requests to Blockchain.info being made for my LTC wallets.
Code:
14/10/2017 16:21:10.627 [055] [E]Failed to download string from: https://blockchain.info/en/balance?active=LMCkkeTMozFJ4KCSRWLiMTiPPkHwQqbgM2&api_code=b7c16c1f-8a21-4e58-b368-96ae5ea79517
System.Net.WebException: The remote server returned an error: (500) Internal Server Error.
14/10/2017 16:21:10.632 [001] [S]Applying Theme: Blue
14/10/2017 16:21:10.849 [064] [E]Failed to download string from: https://blockchain.info/en/balance?active=Lh9uk9D93jMFfXsBcbqfKBQGwNdd9ySSoU&api_code=b7c16c1f-8a21-4e58-b368-96ae5ea79517
System.Net.WebException: The remote server returned an error: (500) Internal Server Error.
14/10/2017 16:21:10.878 [064] [E]Failed to download string from: https://blockchain.info/en/balance?active=LW8cKMWVEtUVvoQ4ExyoVjQ17ZPhMuKwm8&api_code=b7c16c1f-8a21-4e58-b368-96ae5ea79517
System.Net.WebException: The remote server returned an error: (429) Too Many Requests.
What gives? :-)