I have two concepts for envy: 

An insanely jealous and bitter girl/woman who seeks to enslave others so that they will be as miserable as she is. Her power allows her to infect those who possess even a shred of envy. The virus will intensify that emotion till it consumes their entire psyche the way envy consumed hers. This makes them her mindless drones. Her grasp over her slaves grows weaker the more people she enslaves. 

OR 

A power athlete turned villain and loving it. This person has the ability to constantly one up his or her opponent. No one can beat envy with any attack. If you are strong, Envy will be stronger. It is a modified version of power augmentation. This is a bit similar to what was suggested, but you use a more powerful form rather than a weaker version. Suits envy more imo. The drawback is that he cannot initiate attacks. He has to wait to be attacked before he can retaliate. 

As for lust....

A man who hunts so that he can feed his demonic harem. He prefers feeding them other beautiful women. If he doesn't feed these demons they will eat him up. 

He desires their kisses and caresses as it empowers him. Saying he is addicted is an understatement. He suffers from severe withdrawal symptoms if not given that adoration and physical contact his body craves. The pact gives him insane strength, reflexes and a sharpened sense of smell. When the lovely ladies merge with him he will change into a demon. [s]I got this idea from Shadow Hearts. <.<[/s] [s]Oddly the merging is also represents... oh never mind. PG 13.[/s]

Pride ... 

A man who can modify his body so that he can deflect your attacks. Nothing you do shall be able to hurt him because he is always the last one standing. However he can potentially cause damage to his own internal organs if he pushes himself to the limit. Being so prideful he would always overestimate his capabilities.

That's all I could think of... >.< Pity Gluttony is well covered. I thought it was one of the most interesting to conceptualize.

I was thinking of Gluttony as an anorexic looking teenager with spider queen theme. She will spit corrosive acid that can melt organic matter. The acid softens it such that it reaches a state where she can consume the person or creature whole. Consuming the person will send her metabolism into overdrive and allows her to continue feeding. She will literally eat till she vomits. You know she has been around as you shall find pools of foul smelling acid and half digested remains. Her satiety point is rather scary. 

<.< Wrath is the most challenging for me...