How do you insert additional unicode simbols into text

I want to put engineering symbols into a text on a 2 d drawing. I have found the symbols online in std Unicode lists, but they wont copy and paste to rhino. Is their a way to add additional characters to rhinos Unicode library? Is there a way to create symbols and and them into a text string?
Any ideas?

Hi Leon - you should be able to add these manually with Alt key+Code on a number pad:

for instance = alt+202

Is that what you mean?