"Never seize" or "anti seize" compound on the threads of the bleeder valve will work wonders (remove it completely and coat all the threads) and that rubber cap on over the end will keep road grim from building up.

Specialty Lubricants - Anti-Seize : Permatex® Nickel Anti-Seize Lubricant

Or after you get them broke loose the first and get the brake bleed done. Just dab some grease on the whole thing. It works great like putting a dab of grease on the battery cable ends to keep the corrosion from building up.