Oh my goodness! That is so stressful. Your printer doesn't let you do custom paper size? That doesn't surprise me. They keep trying to make this technology more "user-friendly" for people, so they take out all the complicated options for custom settings. Grrrrr!
Is it possible to use the 4x6 paper setting with your 4.5x6.5 cards and just set the margin for the left side .50 inches bigger than the left side? That way everything would still be centered.
Example:
Left margin: 1.0 inches
Right margin: 0.50 inches
You could do the same thing to make the top and the bottom margins work.
Top margin: 1.0 inches
Bottom margin: 0.50 inches
If your printer allows you to go to 0.25 margins (some of them don't allow this), you could do the following set up to get more text space:
Left margin: 0.75 inches
Right margin: 0.25 inches
Top margin: 0.75 inches
Bottom margin: 0.25 inches
I really think this would work. Maybe you already thought of this, but if you haven't, it could be worth a try. Then again, if it won't let you do custom paper sizes, it might not let you do custom margins. If it doesn't let you do custom margin, you could just have everything indented from the left 0.50 inches.
Other than that - stop cutting by hand! Go into Staples or Office Depot or whatever. They have laser paper cutters. No, this doesn't mean the cut it with a laser. But they line it up with a laser and then there is a huge pressure blade. These work pretty well. They say they work for 500 sheets, but I wouldn't let them do more than 25-50 at a a time. It shouldn't be too expensive and it's way easier than what you are doing.
I love cards and pockets. I didn't use them, but we thought about it. I am sad this is becoming such a nightmare for you. I hope one of my suggestions helps to alleviate your pain. Good luck!