Use painters tape to mask off a panel on your card.
Be very sure to get a good seal at the edges of the tape, ensuring that ink will not seep underneath the edge.
But we all know that the tape is very sticky, and will rip the card. So take the tape, and adhere it to your sleeve a couple of times, then put it on your card.I have found that this leaves just the right amount of tackiness.
Ink the space between the tape....
Remember that when you remove the tape when you are done, do not lift upward, but rather slowly pull the tape horizontally.