Cant give any decent info for messing with these particular scammers, but ive worked in call centres for 4 years so here are a few good general ones for phone style scams:
as above: METAL IS GOD, let the scammers know this, find something from the top of europe where the sun never comes out, dumping it onto the line at random intervals during the conversation then continue on like you didnt hear anything, accuse the scammer of being in league with satan if questioned "if you are hearing voices like that you should speak to your priest etc etc"
Bonus points: Find a local metal band with a singer with a good metal growl, record some kids songs, lords prayer, sex story about gmilfs etc, again, play at random intervals and deny all knoweldge.
Rate the scammer out of 10, compare to the phone manner of previous scammers you have had in the past, professionalism, believability etc, If the scammer comments, get nasty and berate him saying you are only trying to help, if they continue to question get really REALLY emotional, yelling/crying/pleading, tail off saying you are worried about the scammers future and you dont want them to end up dead with a needle in their arms/dying alone because of financial failure etc. (personal fave)
Pretend to be pleasuring yourself
Pleasure yourself. tell the scammer what you are doing and that you are not doing it for personal gratification but to emotionally scar them, complain how unsexy the scammers voice is, and how long it will take you to reach climax.
Bonus: heavily involve your prostate
Chat to the scammer and use google traslate to get some decent insults in hindi/russian/swedish whatever, yell them randomly mid conversation.
Pretend to viciously beat you children/spouse/partner mid conversation. One of my exs and I had a great set up where she would answer the phone, on a cue I would yell "WHO ARE YOU TALKING TO SL*T?!!!" and then we would yell and chuck stuff around the room.
Bonus: Have everything go silent, then nothing but breathing down phone.
Read out a suicide note, pop a balloon, put the phone down on a table and walk away. (Actually had this done to me working in a call centre, 2nd worst call of my life)
Answer every question the scammer asks with "ok dude" and "whut?" pretend to be really stoned
Bonus: Only say "ok dude" and "whut?" for entire converstation, see how long it takes em to work it out.
Go to a website for furrys and read out a couple of the stories found therein to the scammer.
Tell the guy you are cooking dinner/doing whatever and to wait 2 mins, put the phone down, come back in 2 mins, apologise, be really sorry, tell him to wait another 2 mins, repeat until they give up.
My general rule is if you can make the other guy hang up, you have won.
Simplest way though is just to put the phone up against a radio/speaker and get a feedback loop going, then walk away, they will hang up within about 10 seconds every time. Whoah, got a bit carried away, eh, enjoy kiddies