Venting Range Hood into Attic Space, Temporarily
The biggest issue you have venting into the attic is warm, moist air being blown into a somewhat closed area (aside from the grease and particles you have a filter for).  If the attic space you vent into is large, and has good ventilation this shouldn't be an issue.  If you have to vent into a small portion of the attic and it looks like the moist air will get caught by insulation then there might be an issue depending on how much it's used.  

The warm air will condense readily in a cold attic, so knowing that, look around and imagine what the moist air will do.  The other issue is that things can come up and "only temporary" ends up being 3-4 years...  Ultimately you'll have to answer for yourself, but for light use an "only a couple months", it's probably fine.