Unfortunately all land border users who are not somehow exempt from the requirement to have an I-94 (i.e. American citizens and LPRs, visa-exempt Canadians and Bermudians and maybe BCC holders), and who do not already have an I-94 that is valid for the time to be spent in the US, will need to go inside to secondary and pay the $6 to get one. Once you have the I-94, however, you'll normally be admitted by primary inspection on subsequent trips, and perhaps be allowed to enter at Class B Ports of Entry, for as long as that I-94 is still valid. Once it expires you'll need to go inside to secondary to get a new one. A frequent VWP traveller can hence expect to visit secondary not (much) more than once every 90 days.
While an occasional visit to secondary is unavoidable a VWP traveller can reduce the frequency at which you have to do this to twice a year by applying for a B visa, as this extends the validity of the I-94s you receive to 6 months. It also permits extensions to be applied for while in the US if you are unavoidably delayed beyond the expiry of the I-94 you entered with.
I'm not positive how this all interacts with air travel but you may find that if you fly to the US and then subsequently enter by land you may be admitted by primary for the remainder of the (paperless) I-94 you received for the flight (I'd be interested to know if someone has experience contrary to this). If so, a mixture of land border and air travel might keep you out of secondary at the land border altogether.