hi Utku,
afaik it's not possible to create blrel without spel, as a workaround you can pass KEEP argument to url:
+KEEP.zCreateRel=chg
then on page load call background ajax to call webengine op to create relation:
if ("$args.KEEP.zCreateRel" == "chg") <func_here>
and i want to warn that it's not an easy one, if you haven't done this before...
Regadrs,
cdtj