I'm not a pro, but couldn't you remove the rocker arms allowing the valves to close?

Are there timing marks on each cam you could use to line up the balancer with afterwards to get the cams on the correct cam gear?

I had my 4.5 engine apart, with the head and cam off. I wasn't too worried about having the timing chain out of the way. I just lined up the marks afterwards, turned it by hand several times to make sure nothing was hitting and it has been fine since.

__________________
63 220S W111
76 300D W115
2013 VW JSW TDI M6

previously-
73 280 SEL 4.5
86 300E 5 speed
2010 VW Jetta TDI M6