Format legend in NdOverlay to hide dimension label and separator

Hi. I’m trying to hide the dimension prefix ('b: ') from the legend. Preferably that would be the legend title. I know of ‘title_format’ but it does not work. I found the format string in the Dimension holoviews code, but it seems hard-coded.
Via a hooks I can fix this, although it is called twice, once for each sub-element.

import pandas as pd
import holoviews as hv
d0 = pd.DataFrame(data = np.arange(6).reshape((2,3)).T,index=np.arange(3),columns=['a','b'])
h = hv.Dataset(d0)
import holoviews.operation as ho
h = ho.histogram(h,dimension='a',groupby='b').opts(show_legend=True)