motherblogger

That's actually right (I would say, I am a native spanish speaker, but I am not an expert in the field as a scholar would be). I am male, and if I declare my adherence to the feminist movement, I'd say (and I do say it) that "yo soy un hombre feminista" and at the same time I would be grammatically correct (I am a feminist). 

Despite that, my thesis advisor (in a non-linguistic field btw), agrees that we can avoid male bias in spanish language, only by using the existing grammar.

What do I mean? For example, when somebody in spanish speaks about a group composed by females and males, that person usually would use the male form as a "generic", e.g. "us in this room" would be translated with the male form  "nosotros en esta habitación", not acknowledging the women that are also a part of that group.

That happens because there is an implicit subject, and that subject is usually "hombre" (male). If we complete the prior sentence with that info, we would see something like this: "nosotros (los hombres) en esta habitación" (translation: "us (the men) in this room").

If we change that implicit subject, in order to avoid bias, from hombre (men, that in spanish has of course a male form, with the article "el") to, for example, personas (people, that in spanish uses a female form, accompanied by the article "la"), we can speak and write in a non-biased form.

In this way, the phrase "nosotros (los hombres) en esta habitación" (We (the men) in this room), can be changed into "nosotras (las personas) en esta habitación" (We (the people) in this room).

I hope I'm being clear with this, english is only my second language so my explanations can get a bit messy!