How to copy check boxes without having to always change the control cell link

I have a spreadsheet that uses several check boxes to track which documents are available in an online library. Every time I add new documents to the spreadsheet, I drag the last cell (containing the check box) down over the new cells. When I copy the check boxes this way, the cell link remains the same for all check boxes I copy. I then have to fix each of the new check box's "cell links" by right clicking on the object and selecting format control. If I add a couple new documents at a time, It's no big deal to format each of the new check boxes one at a time. However, If I need to add several new docs (50+) and it's a pain to have to right click on every new check box to change the "cell link" field. Is there a way to copy a check box down several columns and have Excel auto calculate/update the cell link?

For Example: If I have a check box in cell A1 with a cell link of $B$1 and I want to copy this cell down 50 columns (to add 50 new check boxes)... I want the "cell link" to change accordingly, $B$2, $B$3, $B$4, $B$5, etc.

Any help is appreciated!

Thanks,
jnlong