I don't think you can, period.
I don't think you can at all legally, or even illegaly anymore. I sold a VW Combi in Mexico 30 years ago when you sort of could...sold it to the brother of a Policia Nacional - so that helped.
I think you will be barred from Mexico for 10 years if you don't export your bikes......something like that, or big fine.
Read the bottom of Mexico Mike's page here...just in case you need
confirmation - he's been there forever and knows about everyhting there is to know about Mexico-------
Expired or Lost Mexican Immigration Visa Permits (FMT) And Car Permits
You could advertise and sell to a traveller but I think you have to take
moto over the border - Mexico is kind of sticky about all this now and all the border crossings have computer hookup so you can't fake them out anymore.
If you are stuck and want to sell/leave here in US for another riders to buy, I could help you for about 4 months, but then I think I'm leaving too. I'm just over the border in New Mexico, from Puerto Palomas, Chihuahua and also in Santa Fe sometimes.
You can't sell in US either, except to someone taking bike over border.
You can sell in Costa Rica, but you won't get a good price because buyer has to pay import tax, but it can be done there. Salvador, Belize, Guata, Honduras I don't know about.