As so often, the context helps decide how to interpret ambiguous grammar.
I think the following indicate that the suffering of the Lord's servant
is in fact "for" or "on behalf of" God's people in Isa 53:5.
v. 10 if he should make him(self) a guilt offering, he will see his
offspring.
v. 11 My servant will justify the many, as he will bear their iniquities
v. 4 he bore our griefs, carried our sorrows
v. 5 the chastening for our peace was upon him [thus our reconciliation
with God brought about by his suffering]
v. 6 the Lord laid on him the iniquity of us all
Not to mention the servant is described as blameless, innocent, etc., in
keeping with the law's requirement that an atoning sacrifice be tamim.
Jim's interpretation is about the best one can do with naturalistic
presuppositions, but it is contraindicated by Isa 52:14 which compares
the servant's sufferings with Israel's suffering of the exile
Just as many were appalled at you [Israel]
So his [the servant's] appearance was marred, etc.
And Israel is never described as without sin, as the servant is here.