If you're being pedantic, it's 33.9 x 10-7 metres per metre per ° C
If you're being really pedantic the metres cancel out and leave you with 33.9 x 10-7 per ° C
So, yes, light years or furlongs would be fine. As would linguini. If you want linguini per furlong per ° C then the number itself is going to change though.