Might I suggest using a type="button" instead of type="submit" for your form? that way you can perform a loop before the form is submitted, then you can document.forms["paypal"].submit(). Of course, you would need to include a <noscript> submit button.

When you create your loop, you need to figure out a way to determine which check box gets which option names. Once you have that figured out (look at my suggestion below the code), change your submit button type to "button" and give it the even onclick="submitForm()". Then define this function in your head. Note that the ????????? needs to be figured out:

Code:
function submitForm(){
    _formInputs=document.getElementsByTagName('inputs');
    _checkboxes=[];
    for(i=0;i<_formInputs.length;i++){
        if(_formInputs[i].type=='checkbox') _checkBoxes.push(_formInputs[i]);
    }
    for(i=o;i<_checkboxes.length;i++){
        if(_checkboxes[i].checked) {
            optionName=????????????????; //I don't know how you'll determine this part.
            optionChoice=_checkboxes[i].parentNode.getElementsByTagName('label')[0].value;
            newPPoption(document.forms["paypal"],optionName,optionChoice);
        }
    }
    document.forms["paypal"].submit();
}
In order to decide the value of optionName, I might suggest using class="Photo_Manipulation" (depending on the group it's in, of course) and use optionName=_checkboxes[i].getAttribute("class"). But don't actually define those classes in the stylesheet. Does that make sense?