Without preparation.

One octave under.

Wooden stick between string 2 & 3.

 

Wooden stick between string 2 & 3.

Blutack between string 1 & 2.

 

Plastic screw between string 2 & 3.

Blutack between string 1 & 2.

on D5 & F5

 

Plastic screws between both "string 1 & 2." and string "2 & 3."

on C5 & Eb5 & F5 

 

(If this sound, then I just need to get more of this type of screws)

 

"The original" way:

1 yen coin 

on Eb5

 

1

2

3

3 Piano Strings on one key.