I'd be interested in joing the ride from Central London to registration. Should be a good warm up.
I route checked this route the other day and would suggest it's a pretty good one depending on Ride London road closures:
There may be better options for London Fields onwards as I don't know that bit as well.
I don't think any of the RL road closures will be in place on the Saturday - they tend to start in the early hours of Sunday.
There isn't really a more pleasant route out from London Fields to Woodford unless you want to spend a lot of time meandering down densely-parked residential streets. Lea Bridge Road
is the only viable one but it's not a lot of fun most of the time. After you've crossed the North Circular (horrible roundabout, though), the road widens a bit and is generally OK until Loughton.
One possible alternative might be to go out through Mile End, Stratford and Leytonstone on the 'superhighway'. At the Green Man roundabout you can then either take the road out through Snaresbrook and South Woodford, joining your route at Woodford itself or fork right, through Chigwell. That's pretty much the way we took the Prologue last time.