I spoke to a Google Ads Implementation Specialist yesterday. He confirmed that the ONLY way to setup Enhanced Conversions is to have form fields passed as URL Parameters to the ‘thank you’ page like this: mywebsite.com**
So, there are only 2 options.
1. Hubspot updates their forms to give us this ability (vote for the feature here: https://community.hubspot.com/t5/HubSpot-Ideas/Google-Enhanced-Conversions-through-HubSpot/idi-p/596191)
2. Use custom embed code as @STaruc noted. Here’s how to do that: https://community.hubspot.com/t5/APIs-Integrations/Include-form-fields-as-redirect-URL-parameters-on-an-embedded/td-p/235041
If I had to guess, and it’s a total guess, I’d say Hubspot will get this feature setup in roughly 6 months time. Might be worth waiting depending on your situation.