You can't retreat subs with only drillers (the Admiral specialist is the exception), but you can gift your sub.
If one of the players is attacking two of the four outposts you mention, you might be able to make a deal.
If you arrive first at outpost A, maybe the other player is willing to turn their sub heading that way into a gift? That way there won't be a fight and you'll receive the drillers that belonged to the opponent.
The favor in return, could be that you turn your sub heading to B into a gift for the other player.
You could also quickly look at the outpost that you'll reach first, and after conquering it, immediately send your drillers to another outpost you want. This way the first outpost is freed for your opponent, and you'll have a stronger force heading to that other outpost you wanted.
Later on, diplomacy might lead to trading outposts. You can disable the shields of an outpost and send away all drillers, making it 'free' to take over by someone else. Be convinced that they'll do something for you in return though!
And if no deal can be reached, you can either trashtalk and have an instant enemy, or take your losses and hope they sympathize with you and want to partner up...