Can not currently be done without a lot more additional programming as well as adding extra database fields to the custom tables to store more values.
If it’s a feature you really need, you could always hire me, or any other decent programmer, to develop that for you. My plugin has lots of built-in hooks to allow other plugins to add additional functions (such as the several cheap extensions I have for it already).
Otherwise, I don’t have plans at this time to add any major new features to this plugin. Being able to add custom fields for collection of “more information” to the sheets and sign-up forms is a major amount of extra coding work for both the admin side and the public side, especially if it’s going to be generic enough to be used by many users of this plugin. But, if you have a very specific need for a very specific extra field that would be used for all sign-ups, and doesn’t need to be super generic and flexible, and depending on how and where you want to see that info, it could be a relatively small custom add-on project, or it could still be rather time consuming.
You can always contact me privately to discuss custom programming projects. I also, on occasion do “subsidized” development (reduced rate) of new features or premium extensions (such as the Calendar View extension), if it’s something that I think other people might be interested in purchasing.