The absolute easiest way to do this is to do it in the font.
Once you export your bmfont, add these icons to the font texture in Photoshop / image editor of your choice.
Edit the bmfont text/xml file and add characters for these sprites, and manually enter the x, y, width & height corrdinates.
That way you will just be able to type the characters.
To make things simpler, you can make your exported texture from bmfont big with a lot of empty space at the bottom and insert your icons in the second half always. If you import the font into a sprite collection, any wasted space introduced from your padding will be removed.
It is a bit painful initially, but ultimately will be really simple to use.