Picasso Transfers will take care of the transfer from La Cañada shopping center to the M4DW square (and vice versa). 
Parking at La Cañada is free and for only 2 euros per ride per person you can use this service. 

Also on the registration day October 10 it is possible to use this transfer. The first shuttle on Wednesday runs from 09: 15 am la Cañada until 04:15 pm.
On all walking days*  the first shuttle leaves at 07:45 am (of course more shuttles will arrive after that time) and the last one leaves at 05:15 pm. 

*Take into account that the 20 kilometers will start only on Thursday 11th of October from 09:15 am, 30 kilometers will start as usual from 08:30 am. All other days the 20 kilometers will start from 09:00 am.

You can board at la Cañada as indicated on this map : Boarding at la Cañada 

Picasso Transfers can also arrange your transfer from and to the airport or another destination, contact them directely for this : or phone +34 663 834 957 (Dutch, English, Spanish, German).