Kiki you can substitute ingredients, as long as they have similar or identical associations or correspondences.
However in your particular case you need something to play the role of physical link of this person .Hence the need of his personal article (I assume you mean article as personal object ).If you purchase just any random object you can not have this physical link ,simply because this object has never come in touch with this person .
Each individual has its own energetical imprint (song )and he /she charges hatever he touches ,wears with this imprint .
This object then can be used to represent this person ,since it has into itself part of this person energy .
What you can do to deal with this problem is to create or purchase a doll that looks similar ,put inside it picture of this person and baptised(named it ) it with his/hers name .
Other option you have is to take any object he/she has come in contact with.
Other way is to cleanse an object and then randomly handle it to him/her and then take it back .Anything that has his/hers DNA shall do too as physical link .