Tell him to stop, drop, and roll!
h34r:
No but in all seriousness, I'd ask medical control if it was safe to remove a few in order to transport. If they say to go for it, maintain ABCs, give oxygen (if he wanted it), carefully remove the cacti (I'm assuming that's what they are), and bandage any wounds after they've been removed. I'd probably only remove enough to make transportation possible. Treat for shock, etc. If he wanted pain relief, I'd request ALS. I'd seriously consider calling ALS anyway regardless (that's just me. I think everybody deserves an ALS workup).
If they (MedCon) said to leave them in (I can't imagine they would, as it would make transport virtually impossible), if he wasn't covered on the right side, transport him in the right lateral recumbent position (or a position of comfort, whatever that may be) after assuring ABCs, applying oxygen, etc. I'd apply bandages to hold the cacti in place.
If he was covered on the right side, and MedCon ordered me to leave them in (I can't imagine they would, but let's just play along for kicks and giggles), I would just create a bed of pillows so that as few of the cacti have pressure on them as possible. Again, this and the last transport decision would ONLY be if MedCon ordered me not to remove them. I don't have a lot of experience, but I don't really see that happening if it impedes transport.