There is an open-source DisplayPort transmitter [1] that apparently supports multiple 2.7 Gbps lanes (albeit using family-specific SERDES/differential transceiver blocks, but I doubt that's avoidable at these speeds). This isn't PCIe, but it's also surprisingly close to PCIe 1.0 (2.5 Gbps/lane, and IIRC they use the same 8b/10b code and scrambling algorithm).

[1] https://github.com/hamsternz/FPGA_DisplayPort