Dynamic linking of SVG's

I am trying to find a way of dowloading bits of an SVG at a time, in seperate SVG files but still look like one SVG picture.
Say i have an SVG that i would like to download, its an SVG map with 3 features, then on a user selection i need to add another two features.
I know i can add all these in one file at the beginning and use JavaScript to turn layers on and off but what i have is 3 features in a database
to start with and then later 2 are added once the client has already downloaded the SVG so rather than render a new SVG with the 2 new features 
and have them download the whole thing again is there any way to link them (a new SVG with just the 2 features linked to the old SVG with
3 features) but make them appear as one picture.
Thanks
Andre