connect three coding sequences with IRES
You might be interested in the Foot and Mouth Disease 2A Peptide, a self-cleaving peptide sequence that can be inserted in between two proteins. The proteins are translated as one sequence, but cleaved at the 2A peptide to form 2 proteins. If I'm reading the source right, they used 4 genes in a row with 2A peptides between them. The 2A peptide has the advantage of being much smaller than most IRES elements, while being more reliable than IRES or internal promoters.