Certo (fruit pectin) won't help. Q-Carbo is simply a dilution product. Read the dilution guidelines linked to in my signature.
Your best option for an employment test is to substitute a clean sample. Substitution products are sold on the web or at most headshops.
Quick Fix is my favorite. http://www.urineluck.com/products/7.html and substitution guidelines are also linked to in my signature.
Hope that helps.
N2