I put together a Sahti recipe of my own back in 2003, way overdoing it on the juniper also (I put the berries in primary, which was a mistake, though I did use branches in the mash tun). It was great (if way resinous) until it went infected.
I'm about an eighth Finnish (kippis!), and sadly my only grand-uncle who might have been able to source some authentic yeast died this Spring. Ah, well. I do have a friend with similar Finnish roots. If I get lucky I'll post here.
Until then I'm reformulating my own recipe with a strong nod in the direction of this one. I live in Alabama, so it's unlikely I'll be able to find any juniper branches worth using, but berries are no problem.