Tinycore is here 12/1/2008! Welcome visitors.
Actually, that method only works on the syslinux family of bootloaders. TC does have generic loading of those as well, but it happens at the extension stage, too late for your purposes.On grub a remaster it is.
Some technical obstacles (if they reside on unknown devices), but it's a slippery slope there. I think soon entry points would be wanted for every step of the boot process, bringing unnecessary complexity.