WPA Rule on Equipment:
I would say it's a foul.
1.3 Player’s Use of Equipment
The equipment must meet existing WPA equipment specifications. In general, players are not permitted to introduce novel equipment into the game. The following uses, among others, are considered normal. If the player is uncertain about a particular use of equipment, he should discuss it with the tournament management prior to the start of play. The equipment must be used only for the purpose or in the manner that the equipment was intended. (See 6.16 Unsportsmanlike Conduct.)
I would say it's a foul.