OP did not write to return via Amsterdam, though.
Maybe a bucket list thing no matter the costs, with the finger and imperial mentality on a metric map....

Anyway...a one way trip could work like this:

buy a very cheap used bike with temporary export plates > drive into south of France or further into Spain for a ferry into Morrocco > exit Morocco into Mauritania, get it stamped out of your pass and donate/sell/abandon it inside the no mans land between border posts (or damage it officially "beyond repair" to leave it un-taxed in M or officially sell incl tax) > hitch hike back towards Dakhla airport > return home.

Good luck

BTW: Did anyone yet tried asking a bike rental in Morocco, how much they would pay for a 4-5yr old, used bike of their choice? Or browsed such english speaking ex-pats classified ads, if a private person speaking your language is looking for a bike in Morocco? There must be ways to sell "in advance" to a trusted party in Morocco.
Buying such bike in Europe, drive/export it officially into Morocco (max 5yrs old, +50% import tax) and sell it to the rental shop or via classified ads. As they do not have their own vehicle production and high customs on everything, the M`s used market for vehicles in general has this priced in. Cars worth €2k in Germany are worth €7k in M. Since they only allow to import max 5yr old vehicles, a 4yr old 500ccm would not crush the bank at €3.5-5k. A rental would charge similar for the two weeks including insurance for Morocco.
Calculate this sharply through and look at the immense prices for used vehicles in Morocco. This could be a good deal, in case you manage to show up with low value buying contracts at customs. Margin is cost of fun if negative or worth the hassle if positive.*

At least it would be great experience in oriental negotiation techniques and habits.

Edit: Just quickly ran the numbers on a napkin :
4yr old 500ccm around €5k in Germany > dealer will be happy to invoice "2.5k€" on the export papers, if rest payed in cash > +50% of this invoice amount makes the bike cost 6.250€ legally imported into Morocco + export plates, + insurance during your stay, +fuel and food..

How much would a european rental charge for a 2 week bike trip with Morocco insurance?
How much worth would the 2-3 days long butt hard return trip be, in comparison of spending this precious holiday time in Morocco?