vhdl software emulation
I worked with Seamless last year so I understand what you mean. I remember that it is based on processor support modules (PSPs) which include an instruction set simulator (ISS) and all required interfaces to connect the ISS with a VHDL I/O description of the processor, Denali memory manager for external memories and a special module, which if I am not wrong was a memory mapped text screen. The processor description in VHDL is not needed under this approach.
For thing to work the way you say, I assume you need a tool to automatically generate an ISS (+ any required interfaces with other modules) from a VHDL processor description. I am not aware of such a tool but since these tools are part of a larger environment, I suggest to check with Mentor if they have or plan to release such a tool.