Depending on how you want these bars to look, you can sort-of do it. You'll have to print the bars as character sequences. See the datasheet (page 17,18)
for the complete character set.
If none of those characters will work for you, you can define your own characters in "character generator RAM" on the HD44780 chip. See page 13 of the datasheet:
In the character generator RAM, the user can rewrite character patterns by program. For 5 × 8 dots, eight character patterns can be written, and for 5 × 10 dots, four character patterns can be written.