Nice to hear!

504s can include related services, so one conversation (if he's still struggling with the writing accommodations) might be to see if an assistive technology specialist can come in and give him a few training sessions, to get him up to speed on any tools he needs. Regular, periodic consult with a related service provider (like AT), can be formally written into the 504 plan. This would depend, of course, on how much support he actually needs to access his AT.

And on specific extended time, I typically pair that with reduced workload (items sufficient only to demonstrate mastery of standards/skills)--which, btw, is also an appropriate accommodation for GIEP curriculum compacting purposes.
...pronounced like the long vowel and first letter of the alphabet...