Running forward like the usual Lemming is a bad idea on this map. It is recommended to wait until either the bridge is knocked down by mice rushing to get the cheese first and then the Shaman building a bridge, or waiting until the Shaman puts a weight on the bridge.
If there is a 'noob shaman' or the shaman doesn't place the anvil in time, then the best solution is to run back onto the falling plank, getting as much a grip as possible, then walljumping up the side of the closest pillar. It is possible to jump to the other pillar, however it is very difficult.
The best thing to do here would be to simply place a small, red jointed board above the bridge on the left side.
You can also place ghosted anvils on the left side of the plank. You must be quick though or the added weight of jumping mice on the right will topple it. Around 5 should be efficient in a full room.
Option 2: Add a small board with a red anchor on it and put it anywhere you want. Best place to put is near where the mice spawn. And best, it is stronger than cannons.
0.148 Version: The two support pillars are now ghosted. A duplicate of the original version of this map was made: Map122