It is doable but probably not worth the trouble. If you want to though you first need to understand how a disc is laid out.
Bootable cdrom use the ElTorito format.
Sector 0 starts at the inner ring.
Sector 16 primary volume
Sector 17 Boot record volume
~continues until volume terminates
Booting Catalog - list what boot images are on the disk and sends to the correct image.
Bootable Disk Image 1
Bootable Disk Image 2 - used if multiple boot options,
Cdrom image file - Your data files/programs
The boot information has to be at the inner ring, there is nowhere else the bios will look for it on the disc. So you have to burn that starting at the center. Once it is written and loads the first bootable disk image you can modify that image so that it looks for the data at the outer tracks. The space in between will be empty, unwritten data. This requires a drive that supports packet writing.
You would need to rewrite the boot image file, meaning you have to start with the source code .
This is similar to how simple copy protected cd protect data. If the only thing that knows where the data is located is the executable, then the cd drive has no way to know where to look for the data files.
You could pad out the data all the way to the edge with zeros but it wouldn't boot faster as the image will point to the start of the data, not the part where your programs start. So the cdrom will still have to read the entire track and would actually be slower since it has to read a lot more area.
I really doubt it is worth the effort just for a few seconds faster booting.
If this was not a bootable cd then you could use other methods like multisession to put the data where you want it.