One way would be to work directly with with ActiveX, an example http://www.mathworks.com/support/solutions/en/data/1-17PWC/?solution=1-17PWC.
You will avoid the opening closing of the excel server at each call of xlsread/xlswrite.
Another would be to use some FEX submissions (modifications of the original functions) that don't open/close the connection themselves, making the task faster: xlsread.m for faster data transfer
