It should be possible to make histograms with variable-width bins.  So maybe the data format would be like this:

Bin start       Amount
0               5
10              8
30              12
40              6
50

Or maybe like this:

Bin start       Bin end     Amount
0               10          5
10              30          8
30              40          12
40              50          6

And the amount of things that fall into the bin is the *area* of the box that spans that range on the X axis. So a bin from 1-2 with 3 things in it would produce a bar as tall as a bin from 2-4 with 6 things in it.

http://ask.libreoffice.org/en/question/19816/how-do-i-make-a-histogram-with-unequal-bin-widths/