One of the most popular names of both Krishna and Vishnu is my name, Keshava. There are two common explanations of the name: "one who has Keshu", i.e. long hair, and "the killer of Keshi", a demon killed by Krishna. But in this chapter of the Shanti Parva of the Mahabharata, Krishna gives another explanation of the name:
The rays that emanate from the Sun who gives heat to the world, from the blazing fire, and from the Moon, constitute my hair. Hence do foremost of learned Brahmanas call me by the name of Kesava.
Krishna then tells Arjuna a story of someone who benefited from chanting the name Keshava, namely the sage Dirghatamas. For those who don't know, Dirghatamas was the father of Vishnu's incarnation Dhanvantari and the son of Brihaspati's brother Uchathya. As I discuss in this answer, once Brihaspati impregnated Uchathya's wife Mamata. But there was already a child in Mamata's womb, and this unborn child objected to the impregnation. Bribaspati was angered by this and cursed the child to be blind. As a result, Mamata gave birth to two sons, Brihaspati's son Bharadhwaja and Utathya's son Dirghatamas, who was indeed born blind. In any case, Krishna explains how Dirghatamas was cured of his blindness:
Through this curse of that foremost of Rishis. the child of Utathya was born blind, and blind he remained for a long time. It was for this reason that, that the Rishi, in days of yore, came to be known by the name of Dirghatamas. He, however, acquired the four Vedas with their eternal limbs and subsidiary parts. After that he frequently invoked me by this secret name of mine. Indeed, according to the ordinance as laid down, he repeatedly called upon me by the name of Kesava. Through the merit he acquired by uttering this name repeatedly, he became cured of his blindness and then came to be called by the name of Gotama. This name of mine, therefore, O Arjuna is productive of boons unto them that utter it among all the deities and the high-souled Rishis.
Now Dirgahtamas was one of the sages who heard the Vedas during Tapasya. So my question is, does Dirgatamas ever address Vishnu as "Keshava" in the Vedas?
As you can see in the Rig Veda Anukramani in my answer here, Dirghatamas is the seer of hymns 140-164 of the First Mandala of the Rig Veda, and of these, hymns 154-156 are addressed to Vishnu. But I can't seem to find the name Keshava anywhere.
Was Dirghatamas the seer of hymns in any of the other Vedas, and if so is the name Keshava mentioned in those?