Capital gain on purchase of commercial property

Dear,

A person have sold the residential house property (RHP) in 2011 for Rs. 75 Lacks & had purchased commercial property with that money in 2011 itself. After taking the benefit of indexation on cost of acquisition of RHP the total tax payable becomes Rs. 8 lacks (approx.). The assessee do not have such sum to pay to income tax department??

Is there any way to save tax??

Secondly, The assessee want to pay it in installments, as far as i know there is no option in law to pay tax in installments to the department. Please help in the matter.

Thanks.