For a Summoner 14/Mythic Guardian Tier 6, I selected Impervious Body twice giving DR 10/Epic.
I added Impervious companion:
"Impervious Companion Type: MythicPathAbility Requirements: all of ( at least 1 Mythic Path ~ Guardian Special Ability, at least 1 Mythic Path Ability ~ Impervious Body Special Ability ) and var: MythicLevel at least 3 Description: You can make your bonded creature more resistant to damage. Select one animal companion, eidolon, familiar, or bonded mount. This creature gains any epic damage reduction that you gain from the impervious body path ability. You must have the impervious body path ability to select this ability. Source: Paizo Publishing LLC - Mythic Adventures"
the Eidolon does not show the DR10/Epic, but the Summoner does.
Pathfinder Core Rulebooks (set)
Certain aspects require more effort in coding. The reason I'm flagging this as a feature request is the technicality that it was never coded, and thus is an added feature to implement (Companion support is a BEAST to handle).
This is about an hour worth of work give or take. (Probably less, once I figure out how to do it correctly.) But designing a one-size fits all system is a bear.