To use a limit order as a market order on CubePlus, follow these simple steps:

1. For a buy order, set a limit price above the last traded price (LTP).
2. For a sell order, set a limit price lower than the LTP.

In both cases, your limit order will be executed similar to a market order, as it directs the system to fulfill the order at any price up to the specified limit. 

The benefit of using a limit order is that the set limit price acts as protection, ensuring that the order doesn't get executed beyond that designated price due to sudden price movement.