Oh I see. In such a case an entity function which creates the bitmaps can indeed be useful, I do something similar for a few big textures which I only need in one cutscene too.
You can do that for instance as follows:

BMAP* bmp_big_texture1 = NULL;

void create_big_textures()
{
if(!bmp_big_texture1) bmp_big_texture1 = bmap_create(...);
...
}

Then, when you exit the level you have two options, that is either destroy the bitmaps

ptr_remove(bmp_big_texture1);
bmp_big_texture1 = NULL;

or bmap_purge() (or whatever it is called) the allocated memory. Then you do not have to create the bitmap more than once but still can free unused memory.