If you want to use the Transform SOP as is, and you have no desire to make this into a compile block, the easier thing is to just replace the trivial @PR with:
prim("../transform2", 0, "PR", 0)
or
prim(opinputpath("."), 0, "PR", 0)
for tagging the input SOP generically.
The prim() expression is an old school method to fetch an attribute based on a specific index. Since all the prims have the same value inside the subnet you can use 0 or the first primitive value.
To make it compile safe, use an attrib wrangle as jsmack indicated above.