Gronholm had to withdraw from the second half of last year's Global Rallycross season following a violent crash in practice for the X Games in July.
On Monday he will drive Michal Kosciuszko's Mini in Likenas in Sweden while tutoring the Production class graduate ahead of next weekend's Swedish round of the 2013 WRC.
Motorsport Italia team boss Bruno di Pianto said he was thrilled his team would have the chance to benefit from Gronholm's experience.
"Marcus is a legend in the world of rallying and one of the most inspiring drivers of all time," said di Pianto.
"We'll run for about 100km and Marcus will help Michal with the particular style of driving needed for Sweden based on how much a driver can use or lean on the snow banks.
"He'll also take our Mini John Cooper Works WRC out for a spin and test her limits, which'll allow us to compare his and Michal's data on the 6km test stage, then work on speed-saving details like technical corner entry, mid-corner speed and corner exit.
"I've rarely met a driver as keen to learn and be the best he can be as Michal, so I'm sure that he and the team will benefit a lot from Marcus' masterclass."
Gronholm won the 2000 and '02 titles with Peugeot, and last competed in the WRC full-time in 2007.