The only plug on my Nanocom Evo is the one which connects to the diagnostic port on the Disco2; the OBD shaped type port under the dashboard.
As you've already heard from others, the Disco 2 diagnostics is NOT OBDII compliant. Compliance only became an issue with the release of the Disco 3 in 2005.
Diagnostics on the D2 can be done using either Blackbox Solutions Nanocom or Bearmach Hawkeye; both of which are single dedicated devices, or with Britpart Lynx which I believe requires the addition of a laptop computer. All three devices are within (just) the limitations of the DIYer's pocket.
The other diagnostic device mentioned is "Testbook". This is the main stealer's test system and requires a laptop too, but it also needs a trolley to cart it around on and a whole load of money to buy.
Frankly, assuming you can blag the software from somewhere, the hassle and costs to replicate a Nanocom you'd be just as well off to buy the proper device.