Actually with the right subitism you can do better than that! 🙂
I have two homemade subitisms that can be passed around. Not literary cups, but that doesn’t cause a problem for me at least. They are heavy stone blocks on long flexible leads. My homemade subitisms are very crude, not elegant, and no doubt some of the skilled artisans here could come up with an aesthetically improved equivalent, but it is very utilitarian and on that level has no issues. If you have the interest I suggest maybe making your own heater - get a lab power supply and make your own heating elements because you can make them of any size and it just takes a few moments to make one.
Another option which I got long ago is the battery powered shoyeido kodotu (sp.?) heater but it is more of a novelty for portability than a go-to burner. has a nice small heating area but the plastic is annoying. It has been most useful for introducing friends to the agarwood addiction, as on a few occasions I have lent it out with fresh batteries and a small envelope of chip samples. 🙂