How to connect new bathroom exhaust to power?

My old bathroom wall exhaust fan died (installed 1979) so I'm trying to replace. The problem is the inner space is only 4 inches deep which severely limits my unit choices.

The old unit had the exhaust vent on the top left, power inlet on the top right. The new units have the exhaust vent top left, and power inlet on the bottom left. The current romex is not long enough to snake behind the exhaust vent and down into the bottom power inlet.

Can I use a hidden, in-wall splice to extend the wire and avoid adding a junction box and cover? And then just route the romex wire around the exhaust unit (behind the flexible exhaust duct) into the bottom of the new exhaust fan?

Here's a link to the new fan: https://www.homedepot.com/p/Delta-Breez-Slim-Series-50-CFM-Wall-or-Ceiling-Bathroom-Exhaust-Fan-Energy-Star-SLM50/204347756