Test URL Parameters using "+" in Email Address?

I'm wondering if anyone else has had success or struggles with this as I open a support ticket with Marketo.

To create new test leads using a valid email address, I add a "+" and few characters before the domain (e.g. jessica.dobson+test123@pedowitzgroup.com). I will receive an emails sent to that address at my regular address, but Marketo treats it as a brand new lead, allowing me to fully test lead entries.

I've run into some issues, however, when using that trick when testing forms using URL parameters for hidden fields. Instead of including "+," it adds a space, making the email address invalid which halts any email sends in the flow I'm testing. I tried using the HTML code for "+" (+), but it didn't render the plus sign in the email address either.

Anyone have experience or advice?