You could get trick with the product_info page ...

Make the Product a Gift Certificate for $1.00

Make the spot where price normally shows to read something else or blank when products_id = the Gift Certificate

Make the Add to Cart read something different than the current text so it looks more like you are selecting a Gift Certificate amount than a qty ...

Again, you are making changes based on products_id = XX

Then, the product _info page runs one way for regular products and another for other products ...

If you do the Listings ... you would need to adjust the display for those too based on products_id

Takes a bit of work, but you can use the overrides for most all of this ... :)