To help me lower my gaze when coming across attractive women, especially when they dress provocatively, I find it helpful to visualize myself being rewarded with beautiful women in the akhirah for lowering my gaze. Also to make them more appealing sexually to me (to counter the temptation in front of me), I would not imagine them wearing the full hijab, i.e. they would expose some aurah. Is this permissible?
For your first question, please refer to one of my earlier responses to a related question, titled “Watching Pornography“.
As for your second question, I consider it a great virtue in trying to live a life of piety according to the directives and prescriptions of the Almighty in the hope that in return, God shall fulfill our deepest and most personal desires in the most satisfying manner on the Day of Judgment. Imagining this fulfillment of desires on the Day of Judgment, as a means of controlling ourselves from crossing the prescribed limits of the Almighty during the life of this world, should also be seen as an effort to tempt ourselves into living a pious life which is within the prescribed limits of the Almighty. I, therefore, do not consider such thoughts to be impious.
I hope this helps.
September 8, 2002