I do not have too much RF experience, but I can take a guess at some potential ways to reduce your pad/package parasitics.

1. Try to use "deep-trench isolation" under your pads if available in your process.

2. Do not use ESD devices on the analog pads and handle wafer testing in a controlled environment if possible - however it is best if you use at least some minimal ESD protection.

3. Avoid using bond-wires (i.e. no packaging) and use high-frequency RF probes for testing - these probes are typically gnd-signal-gnd probes for high-performance. Else you may want to use flip-chip packaging.

-Sid