It is not possible for Marketo to pull HTML code from an external site.
The only solution is to push information using the MArketo API.
now you may consider some alternatives such as storing the HTML rows in a custom object in Marketo and use some velocity script token to populate your email.
Thanks Greg for your quick response, this gives me some ideas to pursue!
Rick, you can -- although this does explicitly mean programming -- pull HTML data into a lead field using a webhook.
For example, you can allocate a textarea field on every lead to hold the latest chunk of financial information, et al.
Then this field can be updated using triggered webhooks, which are Marketo's pull API, instead of -- or in addition to -- updated using the REST and SOAP push APIs.