Crossing the LCY is normally easy at the weekends - especially when LCY is closed. (Saturday after 1230L and Sunday before 1230L)
If you are a single fixed wing don't expect anything further West than the Lea Valley.
If you are twin it is much easier to cross. Especially when LCY is on 28 as the zone between Vauxhall and London Bridge can be transited not above 2000 feet without impacting on 28 departures (normally not higher due to LHR traffic). Sometimes you will be given cleared LEVEL at 2400 feet (remaining VMC of course!) as the go around from both ends is up to 2000 initially and traffic downwind to 10 will be level at 2000 abeam the field (again due to LHR traffic)
When LCY is on easterlies it gets a bit harder as there are no places to hold really - especially from the North. Places likely to be held are 1nm North or South of LCY (to let tower get you across using reduced seperartion in the vicinity of an airport) or hold at the Southern most tip of the Isle of Dogs from the South or Southern most lake on the Lea Valley to the North (not so easy to define though) - then you will be asked to look for the traffic and follow it! (We assume you won't catch the Falcon/146 just airborne - please point it out to me if you can!!!!!)
As said - don't forget Rule 5 at all times - you could end up in trouble in this current security climate if you don't adhere to it. You can be sure someone will see over the congested area and report you.