The only creeping Grevilleas I know of are pretty much ground huggers and don't reach dimensions required to cover the side of a house.

Anybody have any experience growing grevillea firesprite in southern California?

While Australian natives are adapted to very low phosphorus soil conditions, only a minority of them are truly P-sensitive. Others don't need it, but can tolerate it in the soil, especially if the roots have adapted to those conditions (as opposed to sudden fertilization) and depending upon the availability of the phosphorous (some soils have higher fixation levels, making the nutrient less able to be taken up by plants). Protaceae is probably the most sensitive to phosphorous (Grevilleas are included here), as are many members of the Rutaceae family. It is also seen in some Mimoaceae and Fabaceae. I have had to fertilize some Australian plants, but it needs to be done carefully and with the correct ratios for the conditions and species. Although they don't tend to die with some deficiencies of Nitrogen, Potassium and micronutrients, their growth rate can be slowed. Plants that are being grown in areas where they are likely to experience P-toxicity often respond very well to supplements of chelated iron or iron sulphate.

Peacock Horticultural Nursery in Sebastopol generally has a good selection. MVQ in my experience is about 4 x 4.