I'm another who is letting it go.
One of my twin boys is like this.All 3 are avid readers,dd adores literacy,dtwin 2 likes it and has lovely spelling,punctuation and handwriting(is often writing stories,in notebooks etc).
Dtwin1 year 4(who actually has an amazing imagination)not so much.I get a bit miffed that more isn't done to entice kids like this but not much you can do at home imvho.
Said twin is left handed and often says his hand hurts which puts him off however he reads avidly,has good handwriting and I'm simply ensuring his spelling,punctuation are good too.He will have his day and go be honest I get fed up with this every child must be an amazing creative writer thing,all adults aren't.
As long as DS has super spelling,punctuation and handwriting I'll be happy.I'm convinced he'll be more of a science writer and will focus on maths and science subjects instead of Eng Lit like me at school.
Alphabet Glue has some great book making and fun,short creative writing ideas.We'll do a few of those over the hols (story rocks)and spelling,punctuation work books which he doesn't mind as it doesn't involve pages of writing.We have all the story cubes too.
We have the Usborne How to Write Stories mentioned further down but it is still a chore for him,the other two love their copy.
Short and sweet,fun, on his own terms is what DS can cope with.