I've figured out how to compile the RTL in Xilinx ISE Webpack9.2i and Altera Quurtus II 7.1. (It just took a few simple RTL-edits.)
But what about the JTAG-debug unit? It seems to use the Lattice's JTAG-block. Can I just replace this with a generic JTAG TAP-controller, and then use a Xilinx-hosted Mico32 with a Lattice download-cable?