Sound Fonts: splitting and recombining SF2 files

Two part problem:

Problem One (solved)
How do you break up a soundfont into its constituent parts?
I succeeded in extracting the guitar from FluidR3GM.sf2 using a small program called SF2Splitter.exe. I called the extracted file guitar.sf2
I've downloaded a piano soundfont called pianissimum.sf2
OK so far so good.

Problem Two (unsolved)
I want to combine the pianissimum.sf2 file with the newly created guitar.sf2 file. Now, I know what you're thinking, FluidR3GM.sf2 has a piano within it. Yes but I really like the pianissimum.sf2 soundfont. At this stage it's obvious I want to create a single soundfont with the two files: guitar.sf2 and pianissimum.sf2

Using the SF2Splitter.exe program takes no more than 30 seconds to use. It would be really great if there was an equally fast, easy and small program that puts two (or more) SF2 files together. (There's Humpty-Dumpty joke in there somewhere.)

Any suggestions?

David