He also had a history of really heavy basses like his Wal double neck. This goes back a "few" years, but I thought he had a bass like you posted made solid and he mostly sat with it. The bridge pickup was also as close to the bridge as humanly possible to get a very bright sound.
He very well may have had one made specifically for him, but that's not what Warwick sells to the public. He's an eccentric, for sure! I really dig him, though, and it's been interesting seeing the progression from that double neck Wal to the single neck Wal and Status to the 6-string acoustic and eventually to the Warwick.