Hi jdrossos, DennisC +
it is not that easy to make the knocker to knock when making an Extraball. The problem is:
To make the knocker to knock --- just "a shot of electricity" (current flowing just a short period of time) is needed --- when making an "Extraball" the Extraball-Relay pulls in and stays pulling for a long time. We cannot hook-up the knocker-coil parallel to the Coil on Extraball-Relay - the knocker would stay pulling - overheating - melting - damaged / ruined.

I live in Europe - rather easy to buy "Finder Relays" --- what You want could be done with Finder Relays --- see here https://www.finder-relais.net/en/finder-relays-series-85.pdf and here https://www.finder-relais.net/en/finder-relays-series-40.pdf
The Finder (series-40 - especially the) 40.52.8.006.0000 / 40.52.8.012.0000 / 40.52.8.024.0000 / 40.52.8.048.0000 / 40.52.8.110.0000 / 40.52.8.120.0000 / 40.52.8.230.0000 40.52.8.240.000 I like for simple NEW relays running on AC-Current - Voltage 6,12,24,48,(110,120,230), 240. They have two three-bladed Make-and-Brake-Switches.
For an modification (Gottlieb Joker-Poker SS) I bought me an Finder-series-85 - here https://www.finder-relais.net/en/finder-relays-series-85.pdf see on page-3 the function "AI", ON delay. Your "problem" can be solved using an Finder-series-85 relay, function "DI" , function "AI" maybe combined with Finder-series-40.52 relay. Attention: Finder-series-85 relays may cost 40 dollars or more - the 40.52 relays are cheaper - maybe 7 to 10 dollars - BUT A Finder-series-85 relay is needed.

Maybe You want to ask in the SS Tech Generic section https://pinside.com/pinball/forum/forum/technical-help - asking for a solution to the problem
To make the knocker to knock --- just "a shot of electricity" (current flowing just a short period of time) is needed --- when making an "Extraball" the Extraball-Relay pulls in and stays pulling for a long time. We cannot hook-up the knocker-coil parallel to the Coil on Extraball-Relay - the knocker would stay pulling - overheating - melting - damaged / ruined.
Greetings Rolf