Whilst the problem is not a Gavick problem, the Solution is as usual, a Gavick solution!
Rather than using the K2 Category Item view, use GK News Pro GK4 to display your category layouts.
The News Pro module allows dynamic resizing by width and height and permits cropping. Full flexibility.
To be perfectly honest, K2 and K2Store become a very powerful tool for an e-commerce website when combined with the power and support of Gavick Templates and Extensions:
I will put an example URL here but I haven't read the rules yet so if it gets removed by moderators I apologise.
Fleurs de Style:
http://www.fleurs-de-style.com/