Cedato Players support six custom macros. 
Each macro is mapped from the player to the Demand item. 
On vast url add the follow: [CUSTOM1] ... [CUSTOM6]
On player call add the param &c1={{VALUE1}} ... &c6={{VALUE6}}
[CUSTOM1] will be replaced with {{VALUE1}} 
*Value must be url encoded
**Note that we don't validate or store the macros being passed from a player to the demand partners
Let's assume your playerId: XXXX so the tag will look like: