100 % cenvat credit

Dear Sir,

1)A proprietory firm is carrying on trading activities in yarn.They are yarn dealers for many yarn manufacturers.
2)They also get commission on sale of their yarn products every month.
3)No other actvity is carried on except yarn trading & commission income.
4)Proprietory firm has incurred foll: common expenditure in carrying out above two activities from same premises:
---i)telephone /mobile exp
---ii)audit fees/c.a.consulting fees
---iii)constructon of office premises(major renovation rs.4 lacs)---eligible for 100% credit
---iv)office insurance ---eligible for 100% credit

query:1)since firm is carrying out only one taxable service (other being trading of yarn)whether cen.credit on above expenditure can be claimed proportionately in ratio of yarn trading & yarn commission ?

2)since there is only one taxable services whether whole amt. of cenvat credit can be claimed agt. ser.tax payable on commission output services?

3)If no, then in what manner?

smehta