Excel -viewer select cells for SUM

Help,

What I need appears basic but browsing through other questions I don't see it asked/answered. I'm organizing contractor's bids on projects. Column 'A" is a name, columns b, c, d are his various bids. I know I can use the sum function to combine his bids in another column. However I want the person viewing the table to be able to select which bids are used in the sum instead of all. The viewer should be able to select values by changing the font or shading, not rewriting the formula. Written in english the formula would be: Sum B3:D3 only if BOLD. I can also add hidden columns if necessary.

Thanks