oooh ?? tell me more ?? he didnt bite the order of the spider bait... need more ammo ...
I think it boils down to whether the player wants it to happen for the character or not. Because the endorsement of a family daimyo, who is also the daughter of a god, and the support of a grandmaster (kind of a family daimyo) should quiet any worries.
But if you need need some IC ammo, because Ishiki wants to hear some arguments:
• Ishiki, ronin or not, has proven his worth to the Spider Clan by winning a Shourido competition that is endorsed by the Regent and the Imperial Families as hosts of the Winter Court. So it is quite a big deal.
• Children will look up to him, because he wields a famous Gyushi blade (famous among the Spider, at least).
• As for him being a traitor; the Dragon take no issue with the Spider worshipping the Dragon traitor Agasha Kyoso. Compared to what she did, Ishiki's treason is small.
• Former Kitsuki daimyo, Empress Iweko, invited (Mirumoto) Taishuu, a tainted traitor to the Dragon into her court, to serve as an ambassador to the Spider Clan. His treason (I think it was subordination) was motivated by a sense of duty, to serve the Dragon Clan, though.
• The Spider take in all kind of ronin and outcasts, surely Dragon among them (just don't mention Kokujin's Order *g*), without this straining the relationship with the Dragon
The important thing is that one year of service is something completely different than swearing fealty. And with all the gestures of friendship between Dragon and Spider this Winter Court, allowing an outcast a way to redemption doesn't sound like the worst.
Another impromptu idea: If he dislikes working among the Spider, even if secretly. If Asina will have an estate with her husband in Crane lands, she could ask that shrines, maybe even a small temple, be built in honour of dead heroes: Mirumoto Miroken, Toku Saiga and Susumu Naishi (maybe even throw in the unnamed Spider Fortune who got deified during Iweko's 10th coronation anniversary). Ishiki would help bless and maintain the shrines or temple (for a year). Of course, the travelling sohei of the Spider would see to it that there will be pilgrims. If there also happens to be built a small dojo with a sohei sensei, Ishiki could help Spider children who come there and learn of Shourido and the ways of the kami. Or other clans' children, too.
Granted, this impromptu idea like shooting a mosquito with a canon, and you might want to discuss any of this within your non-public embassy threads, but if Ishiki's player wants this to happen, there should be ways. Getting Kuroko's approval looks like the hardest part, and this is already done.
If everything fails, remind him that it cost you favours to get Kuroko's approval for this and that your good name is on the line. But you would have to decide if this is something Asina would do.