The original agreement was due to end this month, but it is now expected to run until the Friday night clash with Newcastle Falcons at Sixways on March 16.
Brain has been talking with the World Cup-winning former rugby league star's representatives and says the extension is all-but agreed.
"I don't believe it will be a problem," he said ahead of naming his starting line-up for Saturday's vital ERC Challenge Cup Pool 5 match against ASM Clermont-Auvergne at Sixways (3pm).
"What I'm negotiating is a plan which will keep him here for the next six Premiership matches, and then we'll review it after that."
In eight matches since Larder's arrival as defensive consultant, Warriors have conceded 14 scoring penalties and 10 tries - including two "gimmes" against Harlequins, when the opposition visited Worcester's 22 just four times. At the same time, Warriors have scored 16 tries and landed 16 penalties, giving up a total of 110 points and scoring 153.
Brain makes one change to the Warriors starting line-up for Saturday. Mark Tucker returns to the right wing, with Thinus Delport taking a seat among the replacements, while Will Bowley comes on to the bench alongside Thomas Lombard, who missed the match against Wasps through injury.
Warriors won a bonus point in the 29-23 ERC defeat at Clermont in October, but are only three points behind the French side in the Pool 5 table. With the trip to Viadana, next week, a win would go a long way to securing Worcester a home quarter-final place.
The team's performance in the 19-14 defeat at Wasps, last Sunday, underscores a growing belief around Sixways that Warriors have what it takes to climb the Guinness table to safety.
"We have the potential to perform as well as this club has ever performed in the Premiership for the remaining games of the season," he said. "We're unrecognisable from the team that played in the first part of the season. To push a side like Wasps as close as we did was good, but we want to beat them."
In the past two league matches, playing James Brown at fly-half and Shane Drahm at full-back has added a dimension to Warriors' options on the pitch, and he has highlighted Gary Trueman's return to the side as an attacking centre alongside Brown as another positive.
"He has his heart and soul in the club," he said of the 26-year-old. "His future's stuck firmly on the success of this club on the pitch. I'm glad to see him playing pretty well. He'll need to keep it going, and I'm sure he will."
Team: 01 Darren Morris; 02 Chris Fortey; 03 Chris Horsman; 04 Craig Gillies; 05 Tim Collier; 06 Drew Hickey; 07 Pat Sanderson (c); 08 Kai Horstmann; 09 Matt Powell; 10 James Brown; 11 Marcel Garvey; 12 Gary Trueman; 13 Dale Rasmussen; 14 Mark Tucker; 15 Shane Drahm
Replacements: 16 Tevita Taumoepeau; 17 Aleki Lutui; 18 Will Bowley; 19 Gavin Quinnell; 20 Ryan Powell; 21 Thomas Lombard; 22 Thinus Delport