Thomas is still recovering from an ankle injury he sustained over the winter, and Somerset have given him permission to continue his rehabilitation while working under Delhi head coach Gary Kirsten until April 16.
"The chance arose for him to take on a short-term coaching role at Delhi which is great experience, should he wish to move into coaching in the future," Somerset's director of cricket Matthew Maynard revealed in a statement.
"Medical support to the IPL teams is fantastic and he will be continuing with his rehabilitation while in India.
"He will be back with us on April 16 and will be in contention for selection for our second County Championship of the season which begins on April 26."
The Daredevils have been knocked out of the group stage in four of the last five seasons.