Questions on new shapes and new plugins

[Phan Le <phanl csse monash edu au>]

From reading code and other how-tos stuff, I have learnt that we 2 
kinds of plugins in Dia:
1. Soft: new shapes and sheets are created, put in .dia/shapes & sheets, 
or put in the source and make modifications in Make files. I called it 
soft because it does not require us to change the source much.
2. Hard: you do this when you need new shapes + new properties, and you 
need some kind of thing like new dialog showing non-standard properties 
popped up when double clicking the objects( like in UML). This requires 
us to add source code in /objects and have to  declare our own drawing, 
properties getting functions.

My question is that is it possible to have the mixture of them? Say, I 
have the shapes and sheets already exported in svg, I just want to 
define my own  properties and functions to get the properties displayed 
nicely in a dialog without declaring my own object drawing function.
If possible, which file in the source I need to look at? I had a look at 
 /lib/renderer.* /lin/svgrenderer.c but didnt have a clue.
Cheers,
Phan