Maybe helium leaks less?
Pure hydrogen does not burn let alone explode and released hydrogen or hydrogen mixed with air does need a spark to set it off.
The Hindenburg made quite a few trips before a design flaw caught up with it. Santos-Dumont was making frequent hydrogen blimp flights around 1900, he seemed to have a handle on how-to. It even became a big sport up to 1910 or so with fly-ins in Europe and the US that I know of. During WWI they used hydrogen for observation balloons and Zeppelins where going down in flames was due to enemy fire.
You can get sparks from static but hey they send instrumented balloons up on hydrogen all the time... I wonder how many of those burn up? It takes oxygen (or other oxidizer) mixed with hydrogen to have a problem, you could flush the bag out with dry nitrogen before putting the hydrogen in.
Where to get hydrogen? From a gas supply company. Liquid hydrogen in large quantities used to be about cheap as beer per volume. ;^) It should always be far cheaper than helium.
What's he need a crew up there for anyway?