Thanks to YouTube video comments by arronmunroe, I see Nicktoons Nitro will link in LAN if you send -net parameter to the exe. Mentioned on TP discord to see if the devs would be interested in adding an "network enable" checkbox in the GUI to add this.
If anyone wants to try it now, you can edit the NicktoonNitro.xml in UserProfile folder and replace
<ExtraParameters />
with the following
<ExtraParameters>-net</ExtraParameters>
Also set network IDs in TP game settings to 1 and 2. First boot with net enabled game locks up, but should work fine after that. Also, after a race finishes, player 1 needs to continue first, or else game freezes.