maybe some other forum members (@hiccup?) could help with this question.
The player panel in a bitmapped (xmlc) skin is a construction similar to a spider's web.
Pretty much every item has a dependency on (is anchored to) another item in the panel, and everything must be defined pixel-prefect to make things work. Even the smallest mistake or misalignment can break the skin.
So even while in theory it perhaps could be possible to have the piggy-back skin option containing images to replace images (such as the lastfm images) in the player panel, you would have to know the exact sizes of these images. (including possibly included high-dpi variations of them)
And without having access to the source files of an xmlc skin it's impossible to know that.
The OP might be better off looking at the
Chameleon Dark skin.
Out of the box it looks very similar to the dark fine-tuned skins, but it is a regular XML skin that was designed to adhere to MusicBee's default design as much as possible while making it pretty easy to customise it to one's own colour preferences.
edit
I am only assuming that the lastfm icons in these skins are indeed image files. If they are not, Mayibongwe might be on to something. (not sure, I haven't looked into it)
edit2
Fun fact, I now see that this Chameleon Dark skin of mine is one of the most downloaded ones of all my skin contributions.
And yet the forum post introducing and describing it never received even one response or comment from anyone.
So I am guessing it's absolutely perfect ;-)