build_aggregators() appears to be a pure function, and may thus be invoked against postAggregations without impact on its use for aggregations. More empirically, this works against the Druid tutorial's sample Wikipedia dataset and tutorial:

```python
from pydruid.client import *
import json

# Druid Config
ENDPOINT = 'druid/v2/?pretty'
CLUSTER_URL = 'http://localhost:8083'

druid = pyDruid(CLUSTER_URL, ENDPOINT)

print json.dumps(druid.timeseries(
    dataSource='wikipedia',
    intervals=["2013-01-01/p1y"],
    granularity="day",
    aggregations={
        "count": {"type": "count"}
    },
    postAggregations={
        "countPlusOne": {
            "type": "javascript",
            "fieldNames": ["count"],
            "function": "function(count) { return count + 1; }"
        }}
), indent=2)
```

Am I understanding your concern correctly? Maybe you thought when I said "pass-through" I meant that I made build_aggregations() and build_post_aggregations() both save and return a reference to the same structure.