The documents being filed to establish this new Spanish office/branch or whatever have to name a "managing director" and possibly one or two other officers of the new Spanish company. (In French, the managing director is called the "gérant" - I suspect the Spanish term is similar.)

One of these named individuals (who must be either a Spanish national or someone with the proper visa or residence card to conduct business in Spain) will have to contact the immigration people in Spain on your behalf to get the visa process going. In essence, they will inform the immigration authorities that you are being "offered" a position assisting the new company and will vouch for the fact that you will return home after your year (or whenever).

Admittedly, this is based on how it works in France, but the process seems to be similar in several EU countries that I have had experience dealing with. But the key thing is to get one of those named individuals to start the ball rolling.
Cheers,
Bev