First choice ruckmen Dean Cox and Nic Naitanui are poised to work in tandem this season and Worsfold said both were fit ahead of the side's round one clash with the Brisbane Lions.
However, with Cox restricted by a groin injury last season, and with only two recognised ruckmen on the senior list, Worsfold said Sullivan had been elevated as insurance.
"This [decision] wasn't made with round one in mind," Worsfold said on Tuesday morning. "This decision was made for the season, Will's on our senior list now for the whole year.
"We didn't talk about injuries at all, other than the unlikely case that both our recognised ruckmen were injured.
"He just gives us some insurance if at any stage throughout the year we have an injury to one, or both, of our ruckmen."
Sullivan was recruited for the 2008 season and agreed to a third-year rookie contract at the end of last year, rather than nominating for the NAB AFL Draft.
Worsfold said the mobile big man would not have been elevated if he wasn't ready to play AFL football.
"It's a good reward for Will's performance through the pre-season and the hard work he's put in," Worsfold said.
"Last week against Carlton and in the small amount of ground time he got against Melbourne on the weekend, he showed he could hold up and ruck in the AFL now.
"With only two recognised ruckmen on our senior list, we felt once Will proved that he was ready to step up that he would take that spot on the list."
Sullivan leapfrogs rookies Adam Cockie, who played seven games in 2009, and Callum Wilson, who played four games last season.
With no veterans on its list, West Coast could nominate two rookies for elevation ahead of today's 2pm AEDT deadline.
Meanwhile, the club is awaiting AFL permission to field a number of players in this weekend's WAFL fixtures.
First-year midfielder Koby Stevens looks to be in Worsfold's planning ahead of round one, with the mature-bodied recruit set to line up for WAFL side East Fremantle this weekend to push his claims for an early season debut.
"We've applied to the AFL for a few of our players that haven't played all pre-season games and will benefit from playing this weekend in terms of pushing up for selection in round one," Worsfold said.
"Out of the guys that played against Melbourne on the weekend only [Tom] Swift and Koby Stevens have applied to play."
Dean Cox is a $471,500 ruckman in this season's Toyota AFL Dream Team competition
Nic Naitanui is a $232,400 ruckman
Will Sullivan is a $94,500 ruckman
