An easy workaround I found for that is:
1) Get Tile Layer Pro
2) Paste your .bmp image in Tile Layer Pro
3) Save
4) Fire that badboy back up in YYCHR!
Also, an easy way to make a work area for spriting is opening a second instance of YYCHR with some random rom you've blanked a section out of. That way you can sprite til your heart's content, then simply copy and paste it over to your project.
