You can add a hidden parameter to your checkout page (Shopping > Setup Options > Checkout Options > Additional text insertion areas).
It needs to be added to the HTML.
You specify the order in the VALUE field separated by commas.
Note you need to add ALL the field names that could possibly appear, as the ones you specify will be the only ones added...
<INPUT TYPE=HIDDEN NAME=PARAMS VALUE="a1,a2,a3,b1,b2,b3,over18">