You can take Mears shuttle to Universal from any Disney resort easily.
When you get to MCO, go down to DME as normal, then find the Mears desk NEXT to the DME desk and tell them you want to purchase a RT voucher from xxxxxx resort to Universal. You can then pay for the transfer with a credit card and you will be given a bus ticket.
Then check in for your DME transportation and head to Disney as normal.
The day before you wish to go to Universal, dial "0" from your room phone and ask to be connected to Mears, when Mears comes on the phone tell them you want to go to Universal the next day, approximately what time you want to leave and the name of your resort.
The Mears operator will give you a pickup time and location at Your resort.
Be at the pickup location approximately 15 minutes before they state, and you will be driven to Universal.
This is a shared service and there will be other stops.
Give the driver the voucher you purchased while at MCO.
The driver will tear off half of the ticket.
The other half of the ticket is your return voucher. It should have a phone number on it.
You can schedule your return time when you are dropped off OR you can call the phone number 2 hours before you wish to be picked up and schedule your return over the phone.
Then at the appropriate pickup time be at the same location where you were dropped off and you will be driven back to your resort.
I hope this helps!!
(Oh by the way, you can bypass purchasing the voucher at MCO and just make the Mears reservation over the phone the day before, but you MUST pay the van driver in CASH if you don't prepurchase the voucher.)