You can't arrest on DUI unless there is a test. I would not have tested if there was a family member willing to pick him up. Officers do have that discretion, happens all the time.
Now if he was pulled over in traffic and loaded.....he's going to the pokey. Again, that is what I would have done, having being trained by federal standards (Diplomatic Security) of arrest and application of deadly force; but it's been a long, long time.
HUH You suspect the man to not pass a DUI so you would let him make a call to get picked up. LOL
Ok so now you do that and you are called to an emergency do you ignore your call or stay with him so he might not hurt himself or others.
Of course you do the field test and if he fails you arrest him, Good grief what you want is ridiculous . You do not even want to enforce the laws.