light map textures

I''m almost done with the using of genesis BSP file. I have some problems mapping the lightmap textures because the lightmaps textures are not allways aligned on power of 2. I have textures tehre that are 5x8 5x10 etc. I''m windering what algorithm i have to adopt to preconvert them in power of 2 bitmaps. First aproach that I have taken was to bring the values to closest greater power of 2. so for 5x3 I get 8x4. Then the problem I have I how to spread the pixels from the 5x3 matrix to 8x4 matrix. If I do-it interpolating the adiacent pixels is a lot of work. If I use the nearest, wich one i have to duplicate? For example on colum 1 I have R-G-B (3 pixelx) how to I expnd them on 4 sized storage RRGB RGGB or RGBB Thanks.