It would probably be awesome in soups, but might get lost or add a meaty taste to smoothies.
Do you eat fried eggs? I would try frying them in that - the thought of it is making my mouth water.
Spread it on top of any beef dish; that stuff would turn the lowliest of burgers into a masterpiece.
Since both items are freezable, if you're worried that you won't use it up fast enough, freeze some of it.
I love marrow and I love butter, but would not on my own have thought of mixing them to make a spread. Sounds dreamy.