I am not sure what exactly are you looking for. however, let me say that be careful while choosing any proxy. Most of the researcher use proxies from the available literature and these proxies are often designed for conventional models. In order to use them for islamic finance you need a very thorough analysis. i hope that you come up with your own proxy for islamic baking rather than relaying on other proxies 

There are numbers of studies investigates displace commercial risk you may refer to the following article entitle "Determinants of Displaced Commercial Risk in Islamic Banking Institutions: Malaysia Evidence" this paper is specifically for islamic bank. you may get the article for the following link http://repository.um.edu.my/100868/1/109-433-1-PB.pdf

Some researchers propose a methodology to measure Displaced Commercial Risk in Islamic Banking based on Value at Risk model. The measurement of the actual risks sharing depends on returns smoothing policies of the Islamic bank. For more details please refer to the following article written by Toumi and Viviani at: https://www.researchgate.net/profile/Toumi_Kaouther. Also Arshad et al. at:  http://repository.um.edu.my/100868/1/109-433-1-PB.pdf

Thanks Mohamed for suggesting my article..this is the link on researchgate https://www.researchgate.net/publication/235304089_Actual_Risk_Sharing_Measurement_in_Islamic_Banks?ev=prf_pub

it was a first attempt to measure it.

Novita, please don't hesitate to contact me if you need help.

to cite the article http://www.emeraldinsight.com/doi/abs/10.1108/S2043-9059%282011%290000002021

Article Actual Risk Sharing Measurement in Islamic Banks