The thought of someone putting extensions in a high speed router that was NOT designed for this scares me. In aerospace we also use industrial high speed motors for cutting Nomex honeycomb core.
An employee was killed by an out of balance long cutter (tool) they went right through his chest, severing his aorta…Meaning LONG unbalanced (G2.5 and G1.0) tools can be VERY dangerous projectiles.
PLEASE DON’T DO IT.