The 33-year-old ex-Everton forward has been training with the National League side since the summer.
The free agent has not signed a deal, but has been teaching younger players.
"Yak is courteous, he comes and watches the games, he pays entrance. He's fully on board with what I'm doing and what the club are doing," Garrard said.
Garrard initially got in touch with Yakubu, who lives close to Wood's Hertfordshire ground, through a mutual friend after the forward returned to England following a spell in the Turkish top flight with Kayserispor.
While Garrard has been as yet unable to convince him to sign, Yakubu has been giving advice to 21-year-old Morgan Ferrier - a striker who has scored seven goals in 13 matches this term.
"I'm trying my hardest to get him to sign a contract," Garrard told BBC Three Counties Radio. "But as it stands I don't know where he's going or what he has planned.
"No disrespect to Morgan, Yak has been taking him under his wing the last three or four weeks and as long as he comes in and does that I'm happy to have Yak at the club.
"He teaches things I haven't seen because he's played at the highest level and in fairness to Morgan he's all eyes and ears."
Yakubu is paying for entry to Boreham Wood matches according to boss Luke Garrard, who is "trying his hardest" to sign the former Nigeria striker.