Unfortunately only an extension won't help, because splashy has to be started as soon as possible in the boot process, otherwise you will first see the TC kernel image, probably some text and then the splash screen.
The good news is: It is quite simple to get splashy to work despite of the mentioned problem.
Tasks to follow:
1.) Download splashy 0.3.13 and directfb 1.0.1, compile the latter one first, install it, then splashy. As usual use CFLAGS="-Os -pipe -march=i486 -mtune=i686", splashy with --prefix=/ and make DESTDIR=install_dir_path install.
2.) Recompile the tc kernel with unsetting the option CONFIG_LOGO.
3.) Extract tinycore.gz and copy the files from install_dir_path to the extracted rootfs from tinycore.gz.
4.) Change the file etc/init.d/tc-config in the extracted rootfs folder to startup splashy and do some screen updates while following the commands in the file. For example /sbin/splashy boot, /sbin/splashy_update "progress 10", /sbin/splashy_update "progress 20", and so on.
5.) Be sure to start splashy not too early, depending on your hardware the first entry point can be the section after WAITUSB in the tc-config, otherwise you will get an framebuffer not configured correctly error.
@all: With splashy, directfb and the theme the size of tinycore.gz grows by about 1.6 - 2 MB, maybe it would be an option to use splashy in the future, as it also has the feature to display boot text within the framebuffer image.
Best regards,
Robert