You are able to claim the Eligible Dependant amount of up to $11,327 for your son...however this is reduced by your son's net income. Unfortunately claiming less credit will cause your tax liability to be greater.
Something that may help...you are able to claim the UCCB income as that of your son...yes, it would reduce your Eligible Dependant credit, however if your taxable income is greater than $44,701 then you will save more by reducing your taxable income. Also, the provincial eligible dependant credit generally has a certain amount that the dependant can earn before the provincial credit is reduced, so even if your income is less than $44,701 you should still save on your tax liability.
http://www.cra-arc.gc.ca/tx/ndvdls/tpcs/ncm-tx/rtrn/cmpltng/ddctns/lns300-350/305/rtrn-eng.html
http://www.cra-arc.gc.ca/tx/ndvdls/tpcs/ncm-tx/rtrn/cmpltng/rprtng-ncm/lns101-170/117-eng.html
