Maybe you could have a very short civil war which results in less fasist nationalists taking over. They stay out the war and make the right noises towards Germany, but then they throw themselves in when the war starts to go against the Germans, maybe after North Africa. The advantage they have here is the public might be a bit more warrish, and they have actually got the army to do it. The biggest problem is that the Spanish army is still rubbish. According to wiki: At the end of the Second World War, the Spanish Army counted 22,000 officers, 3,000 NCO and almost 300,000 soldiers. The equipment dated from the Civil War, with some systems produced in Germany during the World War. Doctrine and Training were obsolete, as they had not incorporated the teachings of the Second World War.
Without the civil war, the Spanish army will be a 1930's style army, with lots of infantry, and limited and old armour. However, it isn't hopeless, as lend lease could be redirected from SU and UK. However, this still leads to several problems, as why would the spanish get involved if they knew their army wasn't up to it. Personally, I could see the Spanish secretly approaching the Allies around the time of Torch. This would allow Allied troops, presumly those that went to Italy in 43 getting sent to Spain instead, though allied counter intel would assure the Germans that Greece or Italy was next.
The largest problem is getting troops in Spain and carrying out the troop movements nessecary without the Germans noticing. However, if this can be pulled off without the Germans having a clue until a few days before hand, I could see the allies launching a invasion of Southern France in April/May 1943, though any advances would be small, and could be short lived.
This could allow for an invasion of Normandy in late 43 if the Allies are willing and can find enough men and landing craft; requirements could be less than OTL due to the more boring bits of the Atlantic wall being raided by the nazis for troops; Pas de Calais would be as heavily fortifed as OTL as that was the most likely place for an invasion, as far the Germans are concerned. Net result: Paris could be liberated by Dec 43.