Spray coating asphalt shingles to acheive SRI > 28

We have a steep-sloped roof and cannot use a metal roofing material because of budget restrictions - so we are going to use asphalt shingles. There are asphalt shingles in the market with an SRI >28, however they all seem to be 'architectural' grade and have specific profiles and shapes designed to mimic wood shakes or other traditional roofing materials. We would like to use a plain rectangular-shaped standard 'residential' (inexpensive) type of shingle but no companies seem to manufacture these shingles that meet the SRI requirement. I guess the assumption is if you're looking for a specific SRI value, you probably want the more expensive 'architectural grade' singles - but we don't! My understanding is that the 'cool shingles' that are marketed are applied with a special reflective coating to achieve the SRI >28 requirement. Does anyone know of, or had experience with, applying a cool roof reflective coating to already installed asphalt shingle roofs? For instance, can we installed a standard asphalt shingle roof and then spray it to achieve this LEED credit? Ideally the coating wouldn't interfere with the original look and color of the asphalt shingle. Any ideas? here's a link to the 'SRI >28 architectural grade' shingles available: http://www.coolroofs.org/products/results.php?keyphrase=&select_type=select&type[6]=Shingles+or+Shakes&market_type=&company_name=&brand=&model=&select_color=all&min_solar=&min_solar_3yr=&min_therm=&min_therm_3yr=&sri_init=28&sri_3yr=&slope=&crrc_prod_id=